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.
Edward Liaw (3): Revert "selftests/mm: fix deadlock for fork after pthread_create on ARM" Revert "selftests/mm: replace atomic_bool with pthread_barrier_t" selftests/mm: fix deadlock for fork after pthread_create with atomic_bool
tools/testing/selftests/mm/uffd-common.c | 5 ++-- tools/testing/selftests/mm/uffd-common.h | 3 ++- tools/testing/selftests/mm/uffd-unit-tests.c | 24 ++++++++------------ 3 files changed, 14 insertions(+), 18 deletions(-)
-- 2.47.0.105.g07ac214952-goog
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.
Fixes: e142cc87ac4e ("fix deadlock for fork after pthread_create on ARM") CC: Ryan Roberts ryan.roberts@arm.com Signed-off-by: Edward Liaw edliaw@google.com --- tools/testing/selftests/mm/uffd-unit-tests.c | 7 ------- 1 file changed, 7 deletions(-)
diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index c8a3b1c7edff..3db2296ac631 100644 --- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -241,9 +241,6 @@ static void *fork_event_consumer(void *data) 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, bool with_event, bool test_pin)
/* 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();
This reverts commit e61ef21e27e8deed8c474e9f47f4aa7bc37e138c.
uffd_poll_thread may be called by other tests that do not initialize the pthread_barrier, so this approach is not correct. This will revert to using atomic_bool instead.
Fixes: e61ef21e27e8 ("selftests/mm: replace atomic_bool with pthread_barrier_t") CC: Ryan Roberts ryan.roberts@arm.com Signed-off-by: Edward Liaw edliaw@google.com --- 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, 10 insertions(+), 12 deletions(-)
diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c index 852e7281026e..717539eddf98 100644 --- a/tools/testing/selftests/mm/uffd-common.c +++ b/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; -pthread_barrier_t ready_for_fork; +atomic_bool ready_for_fork;
static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) { @@ -519,8 +519,7 @@ void *uffd_poll_thread(void *arg) pollfd[1].fd = pipefd[cpu*2]; pollfd[1].events = POLLIN;
- /* Ready for parent thread to fork */ - pthread_barrier_wait(&ready_for_fork); + ready_for_fork = true;
for (;;) { ret = poll(pollfd, 2, -1); diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h index 3e6228d8e0dc..a70ae10b5f62 100644 --- a/tools/testing/selftests/mm/uffd-common.h +++ b/tools/testing/selftests/mm/uffd-common.h @@ -33,6 +33,7 @@ #include <inttypes.h> #include <stdint.h> #include <sys/random.h> +#include <stdatomic.h>
#include "../kselftest.h" #include "vm_util.h" @@ -104,7 +105,7 @@ extern bool map_shared; extern bool test_uffdio_wp; extern unsigned long long *count_verify; extern volatile bool test_uffdio_copy_eexist; -extern pthread_barrier_t ready_for_fork; +extern atomic_bool ready_for_fork;
extern uffd_test_ops_t anon_uffd_test_ops; extern uffd_test_ops_t shmem_uffd_test_ops; diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index 3db2296ac631..b3d21eed203d 100644 --- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -774,7 +774,7 @@ static void uffd_sigbus_test_common(bool wp) char c; struct uffd_args args = { 0 };
- pthread_barrier_init(&ready_for_fork, NULL, 2); + ready_for_fork = false;
fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
@@ -791,9 +791,8 @@ static void uffd_sigbus_test_common(bool wp) if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) err("uffd_poll_thread create");
- /* Wait for child thread to start before forking */ - pthread_barrier_wait(&ready_for_fork); - pthread_barrier_destroy(&ready_for_fork); + while (!ready_for_fork) + ; /* Wait for the poll_thread to start executing before forking */
pid = fork(); if (pid < 0) @@ -834,7 +833,7 @@ static void uffd_events_test_common(bool wp) char c; struct uffd_args args = { 0 };
- pthread_barrier_init(&ready_for_fork, NULL, 2); + ready_for_fork = false;
fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); if (uffd_register(uffd, area_dst, nr_pages * page_size, @@ -845,9 +844,8 @@ static void uffd_events_test_common(bool wp) if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) err("uffd_poll_thread create");
- /* Wait for child thread to start before forking */ - pthread_barrier_wait(&ready_for_fork); - pthread_barrier_destroy(&ready_for_fork); + while (!ready_for_fork) + ; /* Wait for the poll_thread to start executing before forking */
pid = fork(); if (pid < 0)
Some additional 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.
Fixes: cff294582798 ("selftests/mm: extend and rename uffd pagemap test") CC: Ryan Roberts ryan.roberts@arm.com Signed-off-by: Edward Liaw edliaw@google.com --- tools/testing/selftests/mm/uffd-unit-tests.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index b3d21eed203d..a2e71b1636e7 100644 --- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -241,6 +241,8 @@ static void *fork_event_consumer(void *data) fork_event_args *args = data; struct uffd_msg msg = { 0 };
+ ready_for_fork = true; + /* Read until a full msg received */ while (uffd_read_msg(args->parent_uffd, &msg));
@@ -308,8 +310,11 @@ static int pagemap_test_fork(int uffd, bool with_event, bool test_pin)
/* Prepare a thread to resolve EVENT_FORK */ if (with_event) { + ready_for_fork = false; if (pthread_create(&thread, NULL, fork_event_consumer, &args)) err("pthread_create()"); + while (!ready_for_fork) + ; /* Wait for the poll_thread to start executing before forking */ }
child = fork();
On Fri, 18 Oct 2024 17:17:21 +0000 Edward Liaw edliaw@google.com wrote:
Subject: [PATCH 0/3] selftests/mm: revert pthread_barrier change and
I simply removed the " and".
Date: Fri, 18 Oct 2024 17:17:21 +0000 X-Mailer: git-send-email 2.47.0.105.g07ac214952-goog
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.
Edward Liaw (3): Revert "selftests/mm: fix deadlock for fork after pthread_create on ARM" Revert "selftests/mm: replace atomic_bool with pthread_barrier_t" selftests/mm: fix deadlock for fork after pthread_create with atomic_bool
I added cc:stable to the first two patches as the thing-being-reverted was cc:stable.
linux-kselftest-mirror@lists.linaro.org
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Andrew Morton -
Edward Liaw