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/selftests-mm-replace-atomic_bool-with-pthread_barrier_t.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@xxxxxxxxxx>
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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20241003211716.371786-2-edliaw@xxxxxxxxxx
Fixes: 8c864371b2a1 ("selftests/mm: fix ARM related issue with fork after
pthread_create")
Signed-off-by: Edward Liaw <edliaw@xxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
selftests-mm-replace-atomic_bool-with-pthread_barrier_t.patch
selftests-mm-fix-deadlock-for-fork-after-pthread_create-on-arm.patch
