+ revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch added to mm-hotfixes-unstable branch

+ revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: Revert "selftests/mm: fix deadlock for fork after pthread_create on ARM"
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Edward Liaw <edliaw@google.com>
Subject: Revert "selftests/mm: fix deadlock for fork after pthread_create on ARM"
Date: Fri, 18 Oct 2024 17:17:22 +0000

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/20241018171734.2315053-1-edliaw@google.com
Link: https://lkml.kernel.org/r/20241018171734.2315053-2-edliaw@google.com
Fixes: e142cc87ac4e ("fix deadlock for fork after pthread_create on ARM")
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-unit-tests.c |    7 -------
 1 file changed, 7 deletions(-)

--- a/tools/testing/selftests/mm/uffd-unit-tests.c~revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm
+++ a/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -241,9 +241,6 @@ static void *fork_event_consumer(void *d
 	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));
 
@@ -311,12 +308,8 @@ static int pagemap_test_fork(int uffd, b
 
 	/* 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();
_

Patches currently in -mm which might be from edliaw@google.com are

revert-selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch
revert-selftests-mm-replace-atomic_bool-with-pthread_barrier_t.patch
selftests-mm-fix-deadlock-for-fork-after-pthread_create-with-atomic_bool.patch