6.6-stable review patch. If anyone has any objections, please let me know.
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From: Edward Liaw edliaw@google.com
commit e61ef21e27e8deed8c474e9f47f4aa7bc37e138c upstream.
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: 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 Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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 +++ b/tools/testing/selftests/mm/uffd-common.c @@ -17,7 +17,7 @@ bool map_shared; bool test_uffdio_wp = true; unsigned long long *count_verify; uffd_test_ops_t *uffd_test_ops; -atomic_bool ready_for_fork; +pthread_barrier_t ready_for_fork;
static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) { @@ -508,7 +508,8 @@ 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 +++ 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" @@ -99,7 +98,7 @@ 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 +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -770,7 +770,7 @@ 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);
@@ -787,8 +787,9 @@ 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) @@ -829,7 +830,7 @@ 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, @@ -840,8 +841,9 @@ 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)