[RHEL8,COMMIT] userfaultfd: selftest: recycle lock threads first

Submitted by Konstantin Khorenko on April 20, 2020, 7:34 a.m.


Message ID 202004200734.03K7Y0WE015256@finist_co8.work.ct
State New
Series "Series without cover letter"
Headers show

Commit Message

Konstantin Khorenko April 20, 2020, 7:34 a.m.
The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.6
commit 03c4276aa59f7d0692999e33de15e759bf1f4b01
Author: Peter Xu <peterx@redhat.com>
Date:   Mon Apr 20 10:33:59 2020 +0300

    userfaultfd: selftest: recycle lock threads first
    Now we recycle the uffd servicing threads earlier than the lock threads.
    It might happen that when the lock thread is still blocked at a pthread
    mutex lock while the servicing thread has already quitted for the cpu so
    the lock thread will be blocked forever and hang the test program.  To fix
    the possible race, recycle the lock threads first.
    This never happens with current missing-only tests, but when I start to
    run the write-protection tests (the feature is not yet posted upstream) it
    happens every time of the run possibly because in that new test we'll need
    to service two page faults for each lock operation.
    Link: http://lkml.kernel.org/r/20180930074259.18229-4-peterx@redhat.com
    Signed-off-by: Peter Xu <peterx@redhat.com>
    Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
    Cc: Shuah Khan <shuah@kernel.org>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Jerome Glisse <jglisse@redhat.com>
    Cc: Zi Yan <zi.yan@cs.rutgers.edu>
    Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
    Cc: Shaohua Li <shli@fb.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    (cherry picked from commit 7eaa8c969efa77127de9a05856eef9e5d22cf487)
    Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
 tools/testing/selftests/vm/userfaultfd.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

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diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 7b8171e3128a..68bbe0eb203e 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -605,6 +605,12 @@  static int stress(unsigned long *userfaults)
 	if (uffd_test_ops->release_pages(area_src))
 		return 1;
+	finished = 1;
+	for (cpu = 0; cpu < nr_cpus; cpu++)
+		if (pthread_join(locking_threads[cpu], NULL))
+			return 1;
 	for (cpu = 0; cpu < nr_cpus; cpu++) {
 		char c;
 		if (bounces & BOUNCE_POLL) {
@@ -622,11 +628,6 @@  static int stress(unsigned long *userfaults)
-	finished = 1;
-	for (cpu = 0; cpu < nr_cpus; cpu++)
-		if (pthread_join(locking_threads[cpu], NULL))
-			return 1;
 	return 0;