Revert "selftests/mm: replace atomic_bool with pthread_barrier_t"

This reverts commit e61ef21.

uffd_poll_thread may be called by other tests that do not initialize the
pthread_barrier, so this approach is not correct.  This will revert to
using atomic_bool instead.

Link: https://lkml.kernel.org/r/20241018171734.2315053-3-edliaw@google.com
Fixes: e61ef21 ("selftests/mm: replace atomic_bool with pthread_barrier_t")
Signed-off-by: Edward Liaw <edliaw@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/uffd-common.c

@@ -18,7 +18,7 @@ bool test_uffdio_wp = true;
 unsigned long long *count_verify;
 uffd_test_ops_t *uffd_test_ops;
 uffd_test_case_ops_t *uffd_test_case_ops;
-pthread_barrier_t ready_for_fork;
+atomic_bool ready_for_fork;
 
 static int uffd_mem_fd_create(off_t mem_size, bool hugetlb)
 {
@@ -519,8 +519,7 @@ void *uffd_poll_thread(void *arg)
 	pollfd[1].fd = pipefd[cpu*2];
 	pollfd[1].events = POLLIN;
 
-	/* Ready for parent thread to fork */
-	pthread_barrier_wait(&ready_for_fork);
+	ready_for_fork = true;
 
 	for (;;) {
 		ret = poll(pollfd, 2, -1);

tools/testing/selftests/mm/uffd-common.h

@@ -33,6 +33,7 @@
 #include <inttypes.h>
 #include <stdint.h>
 #include <sys/random.h>
+#include <stdatomic.h>
 
 #include "../kselftest.h"
 #include "vm_util.h"
@@ -104,7 +105,7 @@ extern bool map_shared;
 extern bool test_uffdio_wp;
 extern unsigned long long *count_verify;
 extern volatile bool test_uffdio_copy_eexist;
-extern pthread_barrier_t ready_for_fork;
+extern atomic_bool ready_for_fork;
 
 extern uffd_test_ops_t anon_uffd_test_ops;
 extern uffd_test_ops_t shmem_uffd_test_ops;

tools/testing/selftests/mm/uffd-unit-tests.c

@@ -774,7 +774,7 @@ static void uffd_sigbus_test_common(bool wp)
 	char c;
 	struct uffd_args args = { 0 };
 
-	pthread_barrier_init(&ready_for_fork, NULL, 2);
+	ready_for_fork = false;
 
 	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 
@@ -791,9 +791,8 @@ static void uffd_sigbus_test_common(bool wp)
 	if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
 		err("uffd_poll_thread create");
 
-	/* Wait for child thread to start before forking */
-	pthread_barrier_wait(&ready_for_fork);
-	pthread_barrier_destroy(&ready_for_fork);
+	while (!ready_for_fork)
+		; /* Wait for the poll_thread to start executing before forking */
 
 	pid = fork();
 	if (pid < 0)
@@ -834,7 +833,7 @@ static void uffd_events_test_common(bool wp)
 	char c;
 	struct uffd_args args = { 0 };
 
-	pthread_barrier_init(&ready_for_fork, NULL, 2);
+	ready_for_fork = false;
 
 	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 	if (uffd_register(uffd, area_dst, nr_pages * page_size,
@@ -845,9 +844,8 @@ static void uffd_events_test_common(bool wp)
 	if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
 		err("uffd_poll_thread create");
 
-	/* Wait for child thread to start before forking */
-	pthread_barrier_wait(&ready_for_fork);
-	pthread_barrier_destroy(&ready_for_fork);
+	while (!ready_for_fork)
+		; /* Wait for the poll_thread to start executing before forking */
 
 	pid = fork();
 	if (pid < 0)