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DRM backend + Session interface + EGL #2

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merged 21 commits into from
May 10, 2017
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ascent12
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@ascent12 ascent12 commented May 2, 2017

This adds the initial support for running on DRM. It also does a lot of the other related stuff such as opening a session with D-Bus, monitoring devices with Udev, and creating a rendering context with GBM/EGL.

This adds a hard dependency on systemd, as logind and sd-bus is being used for the session. This might not be something that some people like, but it can be made optional if/when an alternate way of handling sessions is implemented, like weston and wlc (optionally) uses.

@ddevault
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ddevault commented May 2, 2017

Thanks for all the work! This is a big one, so lots of comments.

Simple fix: style. Braces go on the same line for functions and if statements have mandatory braces (I'll be lenient on the latter only in the case of if (condition) return;).

Less simple: some of the approach is wrong. The code needs to be restructured a bit. The goal of wlroots isn't just to be a drop-in wlc replacement, but to be much more modular and flexible. It'll be up to the user to piece the modules together. More specifically, the udev and logind code should be moved to separate libraries in the top level (or maybe one session library).

Building off of this, the backend should not be setting up resources. Rather than initialize the session, the caller should deal with it and pass wl_backend_drm_init the necessary references. It should also not be initializing the event loop. The ideal function signature is probably wlr_backend_drm_init(wlr_display *display, int gpu_fd). Obviously it also shouldn't release the session, udev, etc in wlr_backend_drm_free.

One advantage to this approach is that, for example, you could initialize two DRM backends to support multiple GPUs. You could also start a DRM backend and a RDP backend, for example. That kind of flexibility is the main goal of wlroots.

Other feedback inline.

CMakeLists.txt Outdated
find_package(Dbus)
find_package(Systemd REQUIRED)
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These should be easy to make optional with the approach I described.

goto error_udev;
}

if (!wlr_drm_renderer_init(&backend->renderer, backend, backend->fd)) {
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At some point I would like to detach this somewhat from the backend as well, but for now it's fine.

[DRM_MODE_CONNECTOR_DSI] = "DSI",
};

static const char *egl_error(void)
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Is EGL applicable to other backends?

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Yeah, EGL can be used to create a renderer for a wl_display.

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Then let's split some of the code into the backend/. I'm okay with the backends creating an OpenGL context for you, but we should still have them share among themselves where appropriate.

}

drmModeFreeResources(res);
}
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Can you split the mostly-DRM code from the mostly-EGL code into two files?

conn->connector_type_id);

list_add(backend->displays, disp);
wlr_log(L_INFO, "Found display '%s'", disp->name);
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Something I'd like to do here is have the backend register the wl_output globals in the display's registry, and have ownership over those resources.

}

static bool display_init_renderer(struct wlr_drm_renderer *renderer,
struct wlr_drm_display *disp)
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Wait is display here an output, not a wl_display? Let's use the output terminology strictly to avoid confusion.


wlr_log(L_ERROR, "Unable to find mode %ux%u@%u", width, height, rate);
return NULL;
}
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Export this function and have the top level call it. If you need to pick one during init, use the preferred mode. Otherwise, leave it up to them. Make a backend-ambiguous way to set the mode either way.

wlr_log(L_ERROR, "Allocation failed: %s", strerror(errno));
goto error;
}
memcpy(disp->modes, conn->modes, sizeof *disp->modes * disp->num_modes);
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style nit: sizeof(*disp->mode)

return NULL;
}

bool wlr_drm_display_modeset(struct wlr_drm_display *disp, const char *str)
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Err, this should probably take a wlr_output_mode or whatever the struct is called.

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This is meant to be the public function I was asking about, right?

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I was just copying weston here, which uses a string. However, I think having a string argument would be quite useful if a compositor just wants to hand a user-defined string (possible straight from a config file) and not have to worry about the details themselves.
We could just have multiple interfaces, or a string to wlr_output_mode function which doesn't do any actual modesetting.

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No thanks. String parsing doesn't belong here. It wouldn't be difficult to take a string and pick it out of the list of modes.

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s/parsing/handling/

}

ret = sd_bus_call_method(session->bus,
"org.freedesktop.login1",
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Style: don't indent with respect to the (, just add a single tab on subsequent lines. Also merge parameters until you hit 80 columns before breaking.

goto error;
}

// This could be done using asprintf, but I don't want to define _GNU_SOURCE
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Better to leave these comments in the PR review, not the source. 👍 to not defining _GNU_SOURCE, though.

struct wlr_session *session,
struct udev_device *dev,
int *fd_out)
{
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Merge parameters until you hit 80 columns on function defs too

return false;
}

int wlr_udev_find_gpu(struct wlr_udev *udev, struct wlr_session *session)
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Better if this function enumerated GPUs instead of just finding the first one.

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ascent12 commented May 2, 2017

@SirCmpwn
Thanks for the feedback.
I figured that there was a bit too much work going on in the backend, and a lot of it would be more generally useful to other parts of the code. I wasn't really sure how the library was going to be structured, so I just left them in inside the backend, expecting them to be split eventually.
I'll get started separating the various parts into their own sections.

@ascent12 ascent12 closed this May 2, 2017
@ascent12 ascent12 reopened this May 2, 2017
@ddevault
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ddevault commented May 2, 2017

Sounds good, thanks!

emersion pushed a commit that referenced this pull request May 30, 2019
If an output is destroyed while an idle_done event is scheduled, it
results in the following Address Sanitizer Output:

==1469==ERROR: AddressSanitizer: heap-use-after-free on address 0x6170000bb668 at pc 0x7f49aaa0c348 bp 0x7ffed5da35b0 sp 0x7ffed5da35a0
WRITE of size 8 at 0x6170000bb668 thread T0
    #0 0x7f49aaa0c347 in schedule_done_handle_idle_timer ../subprojects/wlroots/types/wlr_output.c:265
    #1 0x7f49aa2f875b in wl_event_loop_dispatch_idle (/usr/lib/libwayland-server.so.0+0xa75b)
    #2 0x7f49aa2f8815 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa815)
    #3 0x7f49aa2f739b in wl_display_run (/usr/lib/libwayland-server.so.0+0x939b)
    #4 0x556622dadd51 in server_run ../sway/server.c:216
    #5 0x556622dac25d in main ../sway/main.c:397
    #6 0x7f49aa0d0ce2 in __libc_start_main (/usr/lib/libc.so.6+0x23ce2)
    #7 0x556622d8d09d in _start (/usr/local/bin/sway+0x3909d)

0x6170000bb668 is located 488 bytes inside of 672-byte region [0x6170000bb480,0x6170000bb720)
freed by thread T0 here:
    #0 0x7f49aabc8f89 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:66
    #1 0x7f49aa968fc2 in drm_connector_destroy ../subprojects/wlroots/backend/drm/drm.c:829
    #2 0x7f49aaa0cc52 in wlr_output_destroy ../subprojects/wlroots/types/wlr_output.c:357
    #3 0x7f49aa96d2e9 in scan_drm_connectors ../subprojects/wlroots/backend/drm/drm.c:1265
    #4 0x7f49aa961a59 in drm_invalidated ../subprojects/wlroots/backend/drm/backend.c:135
    #5 0x7f49aaa2e1e9 in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
    #6 0x7f49aa98319f in udev_event ../subprojects/wlroots/backend/session/session.c:52
    #7 0x7f49aa2f87f1 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa7f1)

previously allocated by thread T0 here:
    #0 0x7f49aabc95a1 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:95
    #1 0x7f49aa96b7a2 in scan_drm_connectors ../subprojects/wlroots/backend/drm/drm.c:1114
    #2 0x7f49aa961a59 in drm_invalidated ../subprojects/wlroots/backend/drm/backend.c:135
    #3 0x7f49aaa2e1e9 in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
    #4 0x7f49aa98319f in udev_event ../subprojects/wlroots/backend/session/session.c:52
    #5 0x7f49aa2f87f1 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xa7f1)

SUMMARY: AddressSanitizer: heap-use-after-free ../subprojects/wlroots/types/wlr_output.c:265 in schedule_done_handle_idle_timer
Shadow bytes around the buggy address:
  0x0c2e8000f670: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f680: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f690: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6a0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6b0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
=>0x0c2e8000f6c0: fd fd fd fd fd fd fd fd fd fd fd fd fd[fd]fd fd
  0x0c2e8000f6d0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c2e8000f6e0: fd fd fd fd fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f6f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f700: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c2e8000f710: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb

Remove the idle_done idle timer when the output is destroyed
emersion referenced this pull request in emersion/wlroots Nov 30, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        #1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        #2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        #1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        #2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        #1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        #2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
ddevault pushed a commit that referenced this pull request Dec 1, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        #1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        #2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        #3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        #4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        #5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        #6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        #7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        #8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        #9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        #10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        #11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        #12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        #13 0x559fefb52385 in main ../main.c:67
        #14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        #15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        #1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        #2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        #3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        #4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        #1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        #2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        #3 0x559fefb51ea6 in main ../main.c:20
        #4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
aiqs4 pushed a commit to aiqs4/wlroots that referenced this pull request Dec 19, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
aiqs4 pushed a commit to aiqs4/wlroots that referenced this pull request Dec 19, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
aiqs4 pushed a commit to aiqs4/wlroots that referenced this pull request Dec 19, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
aiqs4 pushed a commit to aiqs4/wlroots that referenced this pull request Dec 19, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
aiqs4 pushed a commit to aiqs4/wlroots that referenced this pull request Dec 19, 2019
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
filips pushed a commit to filips/wlroots that referenced this pull request Mar 15, 2020
This fixes a heap-use-after-free when the session is destroyed before
the backend during wl_display_destroy:

    ==1085==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000000180 at pc 0x7f88e3590c2d bp 0x7ffdc4e33f90 sp 0x7ffdc4e33f80
    READ of size 8 at 0x614000000180 thread T0
        #0 0x7f88e3590c2c in find_device ../subprojects/wlroots/backend/session/session.c:192
        swaywm#1 0x7f88e3590e85 in wlr_session_close_file ../subprojects/wlroots/backend/session/session.c:204
        swaywm#2 0x7f88e357b80c in libinput_close_restricted ../subprojects/wlroots/backend/libinput/backend.c:24
        swaywm#3 0x7f88e21af274  (/lib64/libinput.so.10+0x28274)
        swaywm#4 0x7f88e21aff1d  (/lib64/libinput.so.10+0x28f1d)
        swaywm#5 0x7f88e219ddac  (/lib64/libinput.so.10+0x16dac)
        swaywm#6 0x7f88e21b415d in libinput_unref (/lib64/libinput.so.10+0x2d15d)
        swaywm#7 0x7f88e357c9d6 in backend_destroy ../subprojects/wlroots/backend/libinput/backend.c:130
        swaywm#8 0x7f88e3545a09 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:50
        swaywm#9 0x7f88e358981a in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:54
        swaywm#10 0x7f88e358a059 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:107
        swaywm#11 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)
        swaywm#12 0x7f88e314b466 in wl_display_destroy (/lib64/libwayland-server.so.0+0x9466)
        swaywm#13 0x559fefb52385 in main ../main.c:67
        swaywm#14 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
        swaywm#15 0x559fefb4297d in _start (/home/simon/src/glider/build/glider+0x2297d)

    0x614000000180 is located 320 bytes inside of 416-byte region [0x614000000040,0x6140000001e0)
    freed by thread T0 here:
        #0 0x7f88e3d0a6b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
        swaywm#1 0x7f88e35b51fb in logind_session_destroy ../subprojects/wlroots/backend/session/logind.c:270
        swaywm#2 0x7f88e35905a4 in wlr_session_destroy ../subprojects/wlroots/backend/session/session.c:156
        swaywm#3 0x7f88e358f440 in handle_display_destroy ../subprojects/wlroots/backend/session/session.c:65
        swaywm#4 0x7f88e314acde  (/lib64/libwayland-server.so.0+0x8cde)

    previously allocated by thread T0 here:
        #0 0x7f88e3d0acd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
        swaywm#1 0x7f88e35b911c in logind_session_create ../subprojects/wlroots/backend/session/logind.c:746
        swaywm#2 0x7f88e358f6b4 in wlr_session_create ../subprojects/wlroots/backend/session/session.c:91
        swaywm#3 0x559fefb51ea6 in main ../main.c:20
        swaywm#4 0x7f88e2639152 in __libc_start_main (/lib64/libc.so.6+0x27152)
Xyene added a commit to Xyene/wlroots that referenced this pull request Oct 11, 2020
Fixes swaywm#2425.

wlroots can only handle one outgoing transfer at a time, so it keeps a
list of pending selections. The head of the list is the currently-active
selection, and when that transfer completes and is destroyed, the next
one is started.

The trouble is when you have a transfer to some app that is misbehaving.
fcitx is one such application. With really large transfers, fcitx will
hang and never wake up again. So, you can end up with a transfer list
that looks like this:

| swaywm#1: started | swaywm#2: pending | swaywm#3: pending | swaywm#4: pending |

The file descriptor for transfer swaywm#1 is registered in libwayland's epoll
loop. The rest are waiting in wlroots' list.

As a user, you want your clipboard back, so you `pkill fcitx`. Now
Xwayland sends `XCB_DESTROY_NOTIFY` to let us know to give up. We clean
up swaywm#4 first.

Due to a bug in wlroots code, we register the (fd, transfer data
pointer) pair for swaywm#1 with libwayland *again*, despite it already being
registered. We do this 2 more times as we remove swaywm#3 and swaywm#2.

Finally, we remove swaywm#1 and `free` all the memory associated with it,
before `close`-ing its transfer file descriptor.

However, we still have 3 copies of swaywm#1's file descriptor left in the
epoll loop, since we erroneously added them as part of removing swaywm#2/3/4.
When we `close` the file descriptor as part of swaywm#1's teardown, we
actually cause the epoll loop to wake up the next time around, saying
"this file descriptor has activity!" (it was closed, so `read`-ing would
normally return 0 to let us know of EOF).

But instead of returning 0, it returns -1 with `EBADF`, because the file
descriptor has already been closed. And finally, as part of error-handling
this, we access the transfer pointer, which was `free`'d. And we crash.
emersion added a commit that referenced this pull request Jan 16, 2021
The GBM device needs to be destroyed after the EGL display.

    ==50931==ERROR: AddressSanitizer: SEGV on unknown address 0x7fe40a000049 (pc 0x7fe446121d30 bp 0x60400001bbd0 sp 0x7ffc99c774d0 T0)
    ==50931==The signal is caused by a READ memory access.
        #0 0x7fe446121d30  (/usr/lib/dri/radeonsi_dri.so+0x5f0d30)
        #1 0x7fe4474717bd  (/usr/lib/../lib/libEGL_mesa.so.0+0x177bd)
        #2 0x7fe4474677d9  (/usr/lib/../lib/libEGL_mesa.so.0+0xd7d9)
        #3 0x7fe44cca7b6f in wlr_egl_destroy ../subprojects/wlroots/render/egl.c:379
        #4 0x7fe44ccc2626 in gles2_destroy ../subprojects/wlroots/render/gles2/renderer.c:705
        #5 0x7fe44ccb5041 in wlr_renderer_destroy ../subprojects/wlroots/render/wlr_renderer.c:37
        #6 0x7fe44cd17850 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:296
        #7 0x7fe44ccca4de in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:48
        #8 0x7fe44cd11b21 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:58
        #9 0x7fe44cd125b0 in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:125
        #10 0x7fe44c315e0e  (/usr/lib/libwayland-server.so.0+0x8e0e)
        #11 0x7fe44c3165a6 in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x95a6)
        #12 0x55a2c8870683 in server_fini ../sway/server.c:203
        #13 0x55a2c886cbf2 in main ../sway/main.c:436
        #14 0x7fe44b77c151 in __libc_start_main (/usr/lib/libc.so.6+0x28151)
        #15 0x55a2c883172d in _start (/home/simon/src/sway/build/sway/sway+0x33472d)
emersion referenced this pull request in emersion/wlroots Mar 16, 2021
The original motivation is the following crash:

    #0  0x00007f0ddeddeef5 in raise () at /usr/lib/libc.so.6
    #1  0x00007f0ddedc8862 in abort () at /usr/lib/libc.so.6
    #2  0x00007f0ddedc8747 in _nl_load_domain.cold () at /usr/lib/libc.so.6
    swaywm#3  0x00007f0ddedd7646 in  () at /usr/lib/libc.so.6
    swaywm#4  0x00007f0de033f8de in gles2_get_renderer_in_context (wlr_renderer=0x612000003640) at ../subprojects/wlroots/render/gles2/renderer.c:38
    swaywm#5  0x00007f0de0341675 in gles2_begin (wlr_renderer=0x612000003640, width=3840, height=2160) at ../subprojects/wlroots/render/gles2/renderer.c:186
    swaywm#6  0x00007f0de033b100 in wlr_renderer_begin (r=0x612000003640, width=3840, height=2160) at ../subprojects/wlroots/render/wlr_renderer.c:56
    swaywm#7  0x00007f0de03466ed in gles2_blit_dmabuf (wlr_renderer=0x612000003640, dst_attr=0x60b000150148, src_attr=0x7fff9f9bfde0) at ../subprojects/wlroots/render/gles2/renderer.c:591
    swaywm#8  0x00007f0de033d717 in wlr_renderer_blit_dmabuf (r=0x612000003640, dst=0x60b000150148, src=0x7fff9f9bfde0) at ../subprojects/wlroots/render/wlr_renderer.c:210
    swaywm#9  0x00007f0de04cbc3b in frame_handle_output_commit (listener=0x611000220bc8, data=0x7fff9f9c0050) at ../subprojects/wlroots/types/wlr_screencopy_v1.c:303

The GLES2 renderer assumes it'll have a wlr_buffer to render to.

Instead of accomodating for the edge-case of rendering without a
wlr_buffer, drop wlr_renderer_blit_dmabuf calls and instead use
wlr_renderer_bind_buffer just like the rest of the wlr_renderer users.
wlr_renderer_blit_dmabuf is now unused in wlroots.

The upside is that the new blit_dmabuf function in screencopy is
renderer-agnostic.
emersion added a commit that referenced this pull request Mar 16, 2021
The original motivation is the following crash:

    #0  0x00007f0ddeddeef5 in raise () at /usr/lib/libc.so.6
    #1  0x00007f0ddedc8862 in abort () at /usr/lib/libc.so.6
    #2  0x00007f0ddedc8747 in _nl_load_domain.cold () at /usr/lib/libc.so.6
    #3  0x00007f0ddedd7646 in  () at /usr/lib/libc.so.6
    #4  0x00007f0de033f8de in gles2_get_renderer_in_context (wlr_renderer=0x612000003640) at ../subprojects/wlroots/render/gles2/renderer.c:38
    #5  0x00007f0de0341675 in gles2_begin (wlr_renderer=0x612000003640, width=3840, height=2160) at ../subprojects/wlroots/render/gles2/renderer.c:186
    #6  0x00007f0de033b100 in wlr_renderer_begin (r=0x612000003640, width=3840, height=2160) at ../subprojects/wlroots/render/wlr_renderer.c:56
    #7  0x00007f0de03466ed in gles2_blit_dmabuf (wlr_renderer=0x612000003640, dst_attr=0x60b000150148, src_attr=0x7fff9f9bfde0) at ../subprojects/wlroots/render/gles2/renderer.c:591
    #8  0x00007f0de033d717 in wlr_renderer_blit_dmabuf (r=0x612000003640, dst=0x60b000150148, src=0x7fff9f9bfde0) at ../subprojects/wlroots/render/wlr_renderer.c:210
    #9  0x00007f0de04cbc3b in frame_handle_output_commit (listener=0x611000220bc8, data=0x7fff9f9c0050) at ../subprojects/wlroots/types/wlr_screencopy_v1.c:303

The GLES2 renderer assumes it'll have a wlr_buffer to render to.

Instead of accomodating for the edge-case of rendering without a
wlr_buffer, drop wlr_renderer_blit_dmabuf calls and instead use
wlr_renderer_bind_buffer just like the rest of the wlr_renderer users.
wlr_renderer_blit_dmabuf is now unused in wlroots.

The upside is that the new blit_dmabuf function in screencopy is
renderer-agnostic.
emersion referenced this pull request in emersion/wlroots Jul 8, 2021
[1] and [2] have introduced new wl_array usage in wlroots, but
contains a mistake: wl_array_for_each iterates over pointers to
the wl_array entries, not over entries themselves.

Fix all wl_array_for_each call sites. Name the variables "ptr"
to avoid confusion.

Found via ASan:

    ==148752==ERROR: AddressSanitizer: attempting free on address which was not malloc()-ed: 0x602000214111 in thread T0
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        swaywm#3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        swaywm#4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        swaywm#5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        swaywm#6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        swaywm#7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)
        swaywm#8 0x55cd1a77c9e5 in server_fini ../sway/server.c:218
        swaywm#9 0x55cd1a77893f in main ../sway/main.c:400
        swaywm#10 0x7f6ff04bdb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        swaywm#11 0x55cd1a73a7ad in _start (/home/simon/src/sway/build/sway/sway+0x33a7ad)

    0x602000214111 is located 1 bytes inside of 16-byte region [0x602000214110,0x602000214120)
    freed by thread T0 here:
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        swaywm#3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        swaywm#4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        swaywm#5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        swaywm#6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        swaywm#7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)

    previously allocated by thread T0 here:
        #0 0x7f6ff2236279 in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
        #1 0x7f6ff1066d03 in wl_array_add (/usr/lib/libwayland-server.so.0+0xdd03)

[1]: swaywm#3002
[2]: swaywm#3004
bl4ckb0ne pushed a commit that referenced this pull request Jul 8, 2021
[1] and [2] have introduced new wl_array usage in wlroots, but
contains a mistake: wl_array_for_each iterates over pointers to
the wl_array entries, not over entries themselves.

Fix all wl_array_for_each call sites. Name the variables "ptr"
to avoid confusion.

Found via ASan:

    ==148752==ERROR: AddressSanitizer: attempting free on address which was not malloc()-ed: 0x602000214111 in thread T0
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        #3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        #4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        #5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        #6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        #7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)
        #8 0x55cd1a77c9e5 in server_fini ../sway/server.c:218
        #9 0x55cd1a77893f in main ../sway/main.c:400
        #10 0x7f6ff04bdb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        #11 0x55cd1a73a7ad in _start (/home/simon/src/sway/build/sway/sway+0x33a7ad)

    0x602000214111 is located 1 bytes inside of 16-byte region [0x602000214110,0x602000214120)
    freed by thread T0 here:
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        #3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        #4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        #5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        #6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        #7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)

    previously allocated by thread T0 here:
        #0 0x7f6ff2236279 in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
        #1 0x7f6ff1066d03 in wl_array_add (/usr/lib/libwayland-server.so.0+0xdd03)

[1]: #3002
[2]: #3004
Emantor added a commit to Emantor/wlroots that referenced this pull request Aug 16, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  swaywm#1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  swaywm#2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  swaywm#3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  swaywm#5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  swaywm#6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  swaywm#7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  swaywm#8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  swaywm#9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  swaywm#10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  swaywm#11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  swaywm#14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.

Signed-off-by: Rouven Czerwinski <rouven@czerwinskis.de>
Emantor added a commit to Emantor/wlroots that referenced this pull request Aug 16, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  swaywm#1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  swaywm#2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  swaywm#3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  swaywm#5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  swaywm#6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  swaywm#7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  swaywm#8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  swaywm#9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  swaywm#10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  swaywm#11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  swaywm#14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.
Emantor added a commit to Emantor/wlroots that referenced this pull request Aug 16, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  swaywm#1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  swaywm#2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  swaywm#3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  swaywm#5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  swaywm#6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  swaywm#7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  swaywm#8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  swaywm#9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  swaywm#10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  swaywm#11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  swaywm#14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.
Emantor added a commit to Emantor/wlroots that referenced this pull request Aug 16, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  swaywm#1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  swaywm#2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  swaywm#3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  swaywm#5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  swaywm#6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  swaywm#7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  swaywm#8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  swaywm#9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  swaywm#10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  swaywm#11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  swaywm#14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.
Emantor added a commit to Emantor/wlroots that referenced this pull request Aug 17, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  swaywm#1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  swaywm#2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  swaywm#3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  swaywm#5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  swaywm#6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  swaywm#7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  swaywm#8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  swaywm#9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  swaywm#10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  swaywm#11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  swaywm#13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  swaywm#14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  swaywm#4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.
emersion pushed a commit that referenced this pull request Aug 17, 2021
This should fix the following backtrace, seen on my desktop with one
output disabled:

  #0  atomic_crtc_commit (conn=0x270f5c0, state=0x270f6d0, flags=0, test_only=<optimized out>) at ../backend/drm/atomic.c:178
          drm = 0x1ae9c10
          output = 0x270f5c0
          crtc = 0x0
          modeset = false
          active = false
          mode_id = 43989232
          gamma_lut = 0
          prev_vrr_enabled = <optimized out>
          vrr_enabled = <optimized out>
          atom = {req = 0x270f5c0, failed = 48}
          ok = <optimized out>
  #1  0x00007f1104f33128 in drm_crtc_commit (conn=conn@entry=0x270f5c0, state=state@entry=0x270f6d0, flags=flags@entry=0, test_only=test_only@entry=true) at ../backend/drm/drm.c:339
          __PRETTY_FUNCTION__ = "drm_crtc_commit"
          drm = <optimized out>
          crtc = 0x0
          ok = <optimized out>
  #2  0x00007f1104f34e6c in drm_connector_test (output=output@entry=0x270f5c0) at ../backend/drm/drm.c:488
          conn = 0x270f5c0
          unsupported = <optimized out>
  #3  0x00007f1104f35424 in drm_connector_commit (output=0x270f5c0) at ../backend/drm/drm.c:578
          conn = 0x270f5c0
  #4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
          now = {tv_sec = 7732, tv_nsec = 623813006}
          pre_event = {output = 0x270f5c0, when = 0x7ffecc1be570}
          back_buffer = 0x0
          scale_updated = <optimized out>
          geometry_updated = <optimized out>
          committed = <optimized out>
          event = {output = 0x0, committed = 4401048, when = 0x29f38f0}
  #5  0x0000000000433047 in apply_output_config (oc=oc@entry=0x29f38f0, output=output@entry=0x2710720) at ../sway/config/output.c:431
          wlr_output = 0x270f5c0
          output_box = <optimized out>
  #6  0x0000000000433aaf in apply_output_config_to_outputs (oc=0x2308400) at ../sway/config/output.c:649
          current = 0x29f38f0
          name = <optimized out>
          wildcard = true
          id = "Dell Inc. DELL U2410 F525M9AK0MML\000\060\060\060ACD7\000\000\000\000\000\000\000\220\063\240\002\000\000\000\000L5C\000\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\377\377\377\377\000\000\000\000\355\240E\000\000\000\000\000\377\377\377\377\000\000\000\000@\206+\002\000\000\000\000`\260.\002\000\000\000"
          sway_output = 0x2710720
          tmp = 0x2242030
          seat = <optimized out>
  #7  0x000000000043df6b in cmd_output (argc=<optimized out>, argv=0x2a03390) at ../sway/commands/output.c:108
          error = <optimized out>
          output = <optimized out>
          background = false
  #8  0x0000000000410304 in execute_command (_exec=_exec@entry=0x2975d20 "output * dpms off", seat=0x22a3280, seat@entry=0x0, con=con@entry=0x0) at ../sway/commands.c:291
          res = <optimized out>
          argc = 4
          argv = 0x2a03370
          handler = 0x479230 <handlers+560>
          cmd = <optimized out>
          matched_delim = 0 '\000'
          containers = 0x0
          using_criteria = false
          __PRETTY_FUNCTION__ = "execute_command"
          exec = 0x28f63c0 "output * dpms off"
          head = 0x0
          res_list = 0x2a2e9d0
  #9  0x0000000000418b65 in ipc_client_handle_command (client=client@entry=0x2a6ac80, payload_length=<optimized out>, payload_type=IPC_COMMAND) at ../sway/ipc-server.c:645
          line = <optimized out>
          res_list = <optimized out>
          json = <optimized out>
          length = <optimized out>
          __PRETTY_FUNCTION__ = "ipc_client_handle_command"
          buf = 0x2975d20 "output * dpms off"
  #10 0x000000000041964c in ipc_client_handle_readable (client_fd=<optimized out>, mask=<optimized out>, data=0x2a6ac80) at ../sway/ipc-server.c:267
          pending_length = <optimized out>
          pending_type = <optimized out>
          client = 0x2a6ac80
          read_available = 31
          buf = "i3-ipc\021\000\000\000\000\000\000"
          received = 14
  #11 0x00007f1104fc3492 in wl_event_loop_dispatch () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  #12 0x00007f1104fc1135 in wl_display_run () from /nix/store/ridk7k2ka6dbk4ly7qqjgmc523s4fj89-wayland-1.19.0/lib/libwayland-server.so.0
  No symbol table info available.
  #13 0x000000000041ac10 in server_run (server=server@entry=0x47b0c0 <server>) at ../sway/server.c:261
  No locals.
  #14 0x000000000041a3fc in main (argc=<optimized out>, argv=0x7ffecc1bec68) at ../sway/main.c:395
          verbose = 0
          debug = 0
          validate = 0
          allow_unsupported_gpu = 0
          long_options = {{name = 0x45b516 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x45ee69 "config", has_arg = 1, flag = 0x0, val = 99}, {name = 0x45b51b "validate", has_arg = 0, flag = 0x0, val = 67}, {
              name = 0x45b524 "debug", has_arg = 0, flag = 0x0, val = 100}, {name = 0x45b3ac "version", has_arg = 0, flag = 0x0, val = 118}, {name = 0x45a55c "verbose", has_arg = 0, flag = 0x0, val = 86}, {name = 0x45b52a "get-socketpath",
              has_arg = 0, flag = 0x0, val = 112}, {name = 0x45b539 "unsupported-gpu", has_arg = 0, flag = 0x0, val = 117}, {name = 0x45b549 "my-next-gpu-wont-be-nvidia", has_arg = 0, flag = 0x0, val = 117}, {name = 0x0, has_arg = 0,
              flag = 0x0, val = 0}}
          config_path = 0x0
          usage = 0x45b830 "Usage: sway [options] [command]\n\n  -h, --help", ' ' <repeats 13 times>, "Show help message and quit.\n  -c, --config <config>  Specify a config file.\n  -C, --validate         Check the validity of the config file, th"...
          c = <optimized out>

where the second output is not enabled:

  (gdb) frame 4
  #4  0x00007f1104f600b7 in wlr_output_commit (output=output@entry=0x270f5c0) at ../types/wlr_output.c:837
  837	in ../types/wlr_output.c
  (gdb) p output->enabled
  $3 = false
  (gdb)

The culprit being that since 604674d we
always try to perform a commit, even on a disabled output.
emersion referenced this pull request in emersion/wlroots Oct 29, 2021
Variables on the stack are released when the parent block is closed.
Here, `now` is used outside of the `if` block, causing the following
crash when starting Sway with the headless backend:

    ==49606==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fff94645f90 at pc 0x5558aeae9e29 bp 0x7fff94645df0 sp 0x7fff94645de0
    READ of size 16 at 0x7fff94645f90 thread T0
        #0 0x5558aeae9e28 in handle_present ../sway/desktop/output.c:834
        #1 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        #2 0x7fdc8d54f77f in wlr_output_send_present ../subprojects/wlroots/types/output/output.c:766
        swaywm#3 0x7fdc8d524a28 in output_commit ../subprojects/wlroots/backend/headless/output.c:71
        swaywm#4 0x7fdc8d54d2db in wlr_output_commit ../subprojects/wlroots/types/output/output.c:629
        swaywm#5 0x5558aeb013cb in output_render ../sway/desktop/render.c:1157
        swaywm#6 0x5558aeae549e in output_repaint_timer_handler ../sway/desktop/output.c:544
        swaywm#7 0x5558aeae5f8a in damage_handle_frame ../sway/desktop/output.c:606
        swaywm#8 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        swaywm#9 0x7fdc8d6007d5 in output_handle_frame ../subprojects/wlroots/types/wlr_output_damage.c:44
        swaywm#10 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        swaywm#11 0x7fdc8d54ee84 in wlr_output_send_frame ../subprojects/wlroots/types/output/output.c:720
        swaywm#12 0x7fdc8d54efc3 in schedule_frame_handle_idle_timer ../subprojects/wlroots/types/output/output.c:728
        swaywm#13 0x7fdc8c9dcf5a in wl_event_loop_dispatch_idle (/usr/lib/libwayland-server.so.0+0xaf5a)
        swaywm#14 0x7fdc8c9dcfb4 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xafb4)
        swaywm#15 0x7fdc8c9dabc6 in wl_display_run (/usr/lib/libwayland-server.so.0+0x8bc6)
        swaywm#16 0x5558aeac8e30 in server_run ../sway/server.c:285
        swaywm#17 0x5558aeac3c7d in main ../sway/main.c:396
        swaywm#18 0x7fdc8be35b24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        swaywm#19 0x5558aea8686d in _start (/home/simon/src/sway/build/sway/sway+0x33f86d)
vyivel pushed a commit that referenced this pull request Oct 29, 2021
Variables on the stack are released when the parent block is closed.
Here, `now` is used outside of the `if` block, causing the following
crash when starting Sway with the headless backend:

    ==49606==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fff94645f90 at pc 0x5558aeae9e29 bp 0x7fff94645df0 sp 0x7fff94645de0
    READ of size 16 at 0x7fff94645f90 thread T0
        #0 0x5558aeae9e28 in handle_present ../sway/desktop/output.c:834
        #1 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        #2 0x7fdc8d54f77f in wlr_output_send_present ../subprojects/wlroots/types/output/output.c:766
        #3 0x7fdc8d524a28 in output_commit ../subprojects/wlroots/backend/headless/output.c:71
        #4 0x7fdc8d54d2db in wlr_output_commit ../subprojects/wlroots/types/output/output.c:629
        #5 0x5558aeb013cb in output_render ../sway/desktop/render.c:1157
        #6 0x5558aeae549e in output_repaint_timer_handler ../sway/desktop/output.c:544
        #7 0x5558aeae5f8a in damage_handle_frame ../sway/desktop/output.c:606
        #8 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        #9 0x7fdc8d6007d5 in output_handle_frame ../subprojects/wlroots/types/wlr_output_damage.c:44
        #10 0x7fdc8d6792fb in wlr_signal_emit_safe ../subprojects/wlroots/util/signal.c:29
        #11 0x7fdc8d54ee84 in wlr_output_send_frame ../subprojects/wlroots/types/output/output.c:720
        #12 0x7fdc8d54efc3 in schedule_frame_handle_idle_timer ../subprojects/wlroots/types/output/output.c:728
        #13 0x7fdc8c9dcf5a in wl_event_loop_dispatch_idle (/usr/lib/libwayland-server.so.0+0xaf5a)
        #14 0x7fdc8c9dcfb4 in wl_event_loop_dispatch (/usr/lib/libwayland-server.so.0+0xafb4)
        #15 0x7fdc8c9dabc6 in wl_display_run (/usr/lib/libwayland-server.so.0+0x8bc6)
        #16 0x5558aeac8e30 in server_run ../sway/server.c:285
        #17 0x5558aeac3c7d in main ../sway/main.c:396
        #18 0x7fdc8be35b24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        #19 0x5558aea8686d in _start (/home/simon/src/sway/build/sway/sway+0x33f86d)
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