Revert "selftests/mm: fix deadlock for fork after pthread_create on ARM"

Patch series "selftests/mm: revert pthread_barrier change"

On Android arm, pthread_create followed by a fork caused a deadlock in
the case where the fork required work to be completed by the created
thread.

The previous patches incorrectly assumed that the parent would
always initialize the pthread_barrier for the child thread. This
reverts the change and replaces the fix for wp-fork-with-event with the
original use of atomic_bool.


This patch (of 3):

This reverts commit e142cc87ac4ec618f2ccf5f68aedcd6e28a59d9d.

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

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: e142cc87ac4e ("fix deadlock for fork after pthread_create on ARM")
Signed-off-by: Edward Liaw <[e-mail]>
Cc: Ryan Roberts <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

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

···
 	fork_event_args *args = data;
 	struct uffd_msg msg = { 0 };
 
-	/* Ready for parent thread to fork */
-	pthread_barrier_wait(&ready_for_fork);
-
 	/* Read until a full msg received */
 	while (uffd_read_msg(args->parent_uffd, &msg));
 
···
 
 	/* Prepare a thread to resolve EVENT_FORK */
 	if (with_event) {
-		pthread_barrier_init(&ready_for_fork, NULL, 2);
 		if (pthread_create(&thread, NULL, fork_event_consumer, &args))
 			err("pthread_create()");
-		/* Wait for child thread to start before forking */
-		pthread_barrier_wait(&ready_for_fork);
-		pthread_barrier_destroy(&ready_for_fork);
 	}
 
 	child = fork();