Changes for commit 9c4e6b1a7027f ("mm, mlock, vmscan: no more skipping pagevecs") break this test expectations on the behavior of mlock syscall family immediately inserting the recently faulted pages into the UNEVICTABLE_LRU, when MCL_ONFAULT is passed to the syscall as part of its flag-set.
There is no functional error introduced by the aforementioned commit, but it opens up a time window where the recently faulted and locked pages might yet not be put back into the UNEVICTABLE_LRU, thus causing a subsequent and immediate PFN flag check for the UNEVICTABLE bit to trip on false-negative errors, as it happens with this test.
This patch fix the false negative by forcefully resorting to a code path that will call a CPU pagevec drain right after the fault but before the PFN flag check takes place, sorting out the race that way.
Fixes: 9c4e6b1a7027f ("mm, mlock, vmscan: no more skipping pagevecs") Signed-off-by: Rafael Aquini aquini@redhat.com --- tools/testing/selftests/vm/mlock2-tests.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
diff --git a/tools/testing/selftests/vm/mlock2-tests.c b/tools/testing/selftests/vm/mlock2-tests.c index 637b6d0ac0d0..26dc320ca3c9 100644 --- a/tools/testing/selftests/vm/mlock2-tests.c +++ b/tools/testing/selftests/vm/mlock2-tests.c @@ -7,6 +7,7 @@ #include <sys/time.h> #include <sys/resource.h> #include <stdbool.h> +#include <sched.h> #include "mlock2.h"
#include "../kselftest.h" @@ -328,6 +329,22 @@ static int test_mlock_lock() return ret; }
+/* + * After commit 9c4e6b1a7027f ("mm, mlock, vmscan: no more skipping pagevecs") + * changes made by calls to mlock* family might not be immediately reflected + * on the LRUs, thus checking the PFN flags might race against pagevec drain. + * + * In order to sort out that race, and get the after fault checks consistent, + * the "quick and dirty" trick below is required in order to force a call to + * lru_add_drain_all() to get the recently MLOCK_ONFAULT pages moved to + * the unevictable LRU, as expected by the checks in this selftest. + */ +static void force_lru_add_drain_all(void) +{ + sched_yield(); + system("echo 1 > /proc/sys/vm/compact_memory"); +} + static int onfault_check(char *map) { unsigned long page_size = getpagesize(); @@ -343,6 +360,9 @@ static int onfault_check(char *map) }
*map = 'a'; + + force_lru_add_drain_all(); + page1_flags = get_pageflags((unsigned long)map); page2_flags = get_pageflags((unsigned long)map + page_size);
@@ -465,6 +485,8 @@ static int test_lock_onfault_of_present() goto unmap; }
+ force_lru_add_drain_all(); + page1_flags = get_pageflags((unsigned long)map); page2_flags = get_pageflags((unsigned long)map + page_size); page1_flags = get_kpageflags(page1_flags & PFN_MASK);