The patch titled Subject: selftests/mm: replace atomic_bool with pthread_barrier_t has been added to the -mm mm-hotfixes-unstable branch. Its filename is selftests-mm-replace-atomic_bool-with-pthread_barrier_t.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: replace atomic_bool with pthread_barrier_t Date: Thu, 3 Oct 2024 21:17:10 +0000

Patch series "selftests/mm: fix deadlock after pthread_create".

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.

Update the synchronization primitive to use pthread_barrier instead of atomic_bool.

Apply the same fix to the wp-fork-with-event test.

This patch (of 2):

Swap synchronization primitive with pthread_barrier, so that stdatomic.h does not need to be included.

The synchronization is needed on Android ARM64; we see a deadlock with pthread_create when the parent thread races forward before the child has a chance to start doing work.

Link: https://lkml.kernel.org/r/20241003211716.371786-1-edliaw@google.com Link: https://lkml.kernel.org/r/20241003211716.371786-2-edliaw@google.com Fixes: 8c864371b2a1 ("selftests/mm: fix ARM related issue with fork after pthread_create") 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

tools/testing/selftests/mm/uffd-common.c | 5 +++-- tools/testing/selftests/mm/uffd-common.h | 3 +-- tools/testing/selftests/mm/uffd-unit-tests.c | 14 ++++++++------ 3 files changed, 12 insertions(+), 10 deletions(-)

--- a/tools/testing/selftests/mm/uffd-common.c~selftests-mm-replace-atomic_bool-with-pthread_barrier_t +++ a/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; -atomic_bool ready_for_fork; +pthread_barrier_t ready_for_fork;

static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) { @@ -519,7 +519,8 @@ void *uffd_poll_thread(void *arg) pollfd[1].fd = pipefd[cpu*2]; pollfd[1].events = POLLIN;

- ready_for_fork = true; + /* Ready for parent thread to fork */ + pthread_barrier_wait(&ready_for_fork);

for (;;) { ret = poll(pollfd, 2, -1); --- a/tools/testing/selftests/mm/uffd-common.h~selftests-mm-replace-atomic_bool-with-pthread_barrier_t +++ a/tools/testing/selftests/mm/uffd-common.h @@ -33,7 +33,6 @@ #include <inttypes.h> #include <stdint.h> #include <sys/random.h> -#include <stdatomic.h>

#include "../kselftest.h" #include "vm_util.h" @@ -105,7 +104,7 @@ extern bool map_shared; extern bool test_uffdio_wp; extern unsigned long long *count_verify; extern volatile bool test_uffdio_copy_eexist; -extern atomic_bool ready_for_fork; +extern pthread_barrier_t ready_for_fork;

extern uffd_test_ops_t anon_uffd_test_ops; extern uffd_test_ops_t shmem_uffd_test_ops; --- a/tools/testing/selftests/mm/uffd-unit-tests.c~selftests-mm-replace-atomic_bool-with-pthread_barrier_t +++ a/tools/testing/selftests/mm/uffd-unit-tests.c @@ -774,7 +774,7 @@ static void uffd_sigbus_test_common(bool char c; struct uffd_args args = { 0 };

- ready_for_fork = false; + pthread_barrier_init(&ready_for_fork, NULL, 2);

fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);

@@ -791,8 +791,9 @@ static void uffd_sigbus_test_common(bool if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) err("uffd_poll_thread create");

- while (!ready_for_fork) - ; /* Wait for the poll_thread to start executing before forking */ + /* Wait for child thread to start before forking */ + pthread_barrier_wait(&ready_for_fork); + pthread_barrier_destroy(&ready_for_fork);

pid = fork(); if (pid < 0) @@ -833,7 +834,7 @@ static void uffd_events_test_common(bool char c; struct uffd_args args = { 0 };

- ready_for_fork = false; + pthread_barrier_init(&ready_for_fork, NULL, 2);

fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); if (uffd_register(uffd, area_dst, nr_pages * page_size, @@ -844,8 +845,9 @@ static void uffd_events_test_common(bool if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) err("uffd_poll_thread create");

- while (!ready_for_fork) - ; /* Wait for the poll_thread to start executing before forking */ + /* Wait for child thread to start before forking */ + pthread_barrier_wait(&ready_for_fork); + pthread_barrier_destroy(&ready_for_fork);

pid = fork(); if (pid < 0) _

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