The patch titled Subject: selftests/mm: fix ARM related issue with fork after pthread_create has been added to the -mm mm-hotfixes-unstable branch. Its filename is selftests-mm-fix-arm-related-issue-with-fork-after-pthread_create.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: fix ARM related issue with fork after pthread_create Date: Mon, 25 Mar 2024 19:40:52 +0000

Following issue was observed while running the uffd-unit-tests selftest on ARM devices. On x86_64 no issues were detected:

pthread_create followed by fork caused deadlock in certain cases wherein fork required some work to be completed by the created thread. Used synchronization to ensure that created thread's start function has started before invoking fork.

[edliaw@google.com: refactored to use atomic_bool] Link: https://lkml.kernel.org/r/20240325194100.775052-1-edliaw@google.com Fixes: 760aee0b71e3 ("selftests/mm: add tests for RO pinning vs fork()") Signed-off-by: Lokesh Gidra lokeshgidra@google.com Signed-off-by: Edward Liaw edliaw@google.com Cc: Peter Xu peterx@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

tools/testing/selftests/mm/uffd-common.c | 3 +++ tools/testing/selftests/mm/uffd-common.h | 2 ++ tools/testing/selftests/mm/uffd-unit-tests.c | 10 ++++++++++ 3 files changed, 15 insertions(+)

--- a/tools/testing/selftests/mm/uffd-common.c~selftests-mm-fix-arm-related-issue-with-fork-after-pthread_create +++ a/tools/testing/selftests/mm/uffd-common.c @@ -18,6 +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;

static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) { @@ -518,6 +519,8 @@ void *uffd_poll_thread(void *arg) pollfd[1].fd = pipefd[cpu*2]; pollfd[1].events = POLLIN;

+ ready_for_fork = true; + for (;;) { ret = poll(pollfd, 2, -1); if (ret <= 0) { --- a/tools/testing/selftests/mm/uffd-common.h~selftests-mm-fix-arm-related-issue-with-fork-after-pthread_create +++ a/tools/testing/selftests/mm/uffd-common.h @@ -32,6 +32,7 @@ #include <inttypes.h> #include <stdint.h> #include <sys/random.h> +#include <stdatomic.h>

#include "../kselftest.h" #include "vm_util.h" @@ -103,6 +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 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-fix-arm-related-issue-with-fork-after-pthread_create +++ a/tools/testing/selftests/mm/uffd-unit-tests.c @@ -775,6 +775,8 @@ static void uffd_sigbus_test_common(bool char c; struct uffd_args args = { 0 };

+ ready_for_fork = false; + fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);

if (uffd_register(uffd, area_dst, nr_pages * page_size, @@ -790,6 +792,9 @@ 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 */ + pid = fork(); if (pid < 0) err("fork"); @@ -829,6 +834,8 @@ static void uffd_events_test_common(bool char c; struct uffd_args args = { 0 };

+ ready_for_fork = false; + fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); if (uffd_register(uffd, area_dst, nr_pages * page_size, true, wp, false)) @@ -838,6 +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 */ + pid = fork(); if (pid < 0) err("fork"); _

Patches currently in -mm which might be from edliaw@google.com are

selftests-mm-sigbus-wp-test-requires-uffd_feature_wp_hugetlbfs_shmem.patch selftests-mm-fix-arm-related-issue-with-fork-after-pthread_create.patch