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.
Updated the synchronization primitive to use pthread_barrier instead of atomic_bool.
Applied the same fix to the wp-fork-with-event test.
Edward Liaw (2): selftests/mm: replace atomic_bool with pthread_barrier_t selftests/mm: fix deadlock for fork after pthread_create on ARM
tools/testing/selftests/mm/uffd-common.c | 5 +++-- tools/testing/selftests/mm/uffd-common.h | 3 +-- tools/testing/selftests/mm/uffd-unit-tests.c | 21 ++++++++++++++------ 3 files changed, 19 insertions(+), 10 deletions(-)
-- 2.46.1.824.gd892dcdcdd-goog
Swaps 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.
Fixes: 8c864371b2a1 ("selftests/mm: fix ARM related issue with fork after pthread_create") 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, 12 insertions(+), 10 deletions(-)
diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c index 717539eddf98..852e7281026e 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; -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); diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h index a70ae10b5f62..3e6228d8e0dc 100644 --- a/tools/testing/selftests/mm/uffd-common.h +++ b/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; diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index b3d21eed203d..3db2296ac631 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 };
- 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 wp) 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 wp) 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 wp) 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)
On Android with arm, there is some synchronization needed to avoid a deadlock when forking after pthread_create.
Fixes: cff294582798 ("selftests/mm: extend and rename uffd pagemap test") Signed-off-by: Edward Liaw edliaw@google.com --- tools/testing/selftests/mm/uffd-unit-tests.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index 3db2296ac631..c8a3b1c7edff 100644 --- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -241,6 +241,9 @@ 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));
@@ -308,8 +311,12 @@ 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();
On Thu, 3 Oct 2024 21:17:09 +0000 Edward Liaw edliaw@google.com wrote:
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.
Updated the synchronization primitive to use pthread_barrier instead of atomic_bool.
Applied the same fix to the wp-fork-with-event test.
Edward Liaw (2): selftests/mm: replace atomic_bool with pthread_barrier_t selftests/mm: fix deadlock for fork after pthread_create on ARM
These fixes have different Fixes: targets, which might cause backporting issues - some kernels might end up with one patch and not the other. Was this intended? Is it OK?
linux-kselftest-mirror@lists.linaro.org
-
Andrew Morton -
Edward Liaw