[Devel] [PATCH vz8 01/42] userfaultfd: selftest: recycle lock threads first

[Andrey Ryabinin]

From: Peter Xu <peterx at redhat.com>

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 at redhat.com>
Acked-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
Cc: Shuah Khan <shuah at kernel.org>
Cc: Mike Kravetz <mike.kravetz at oracle.com>
Cc: Jerome Glisse <jglisse at redhat.com>
Cc: Zi Yan <zi.yan at cs.rutgers.edu>
Cc: "Kirill A . Shutemov" <kirill at shutemov.name>
Cc: Shaohua Li <shli at fb.com>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: "Dr . David Alan Gilbert" <dgilbert at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

https://jira.sw.ru/browse/PSBM-102938
(cherry picked from commit 7eaa8c969efa77127de9a05856eef9e5d22cf487)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

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;
 }
 
-- 
2.25.3