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

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

[Andrew Morton]

The patch titled
     Subject: selftests/mm: fix deadlock for fork after pthread_create on ARM
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     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/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: selftests/mm: fix deadlock for fork after pthread_create on ARM
Date: Thu, 3 Oct 2024 21:17:11 +0000

On Android with arm, there is some synchronization needed to avoid a
deadlock when forking after pthread_create.

Link: https://lkml.kernel.org/r/20241003211716.371786-3-edliaw@google.com
Fixes: cff294582798 ("selftests/mm: extend and rename uffd pagemap test")
Signed-off-by: Edward Liaw <edliaw@google.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/uffd-unit-tests.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/tools/testing/selftests/mm/uffd-unit-tests.c~selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm
+++ a/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -241,6 +241,9 @@ 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));
 
@@ -308,8 +311,12 @@ 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

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