The patch titled
Subject: mlock: fix mlock count can not decrease in race condition
has been added to the -mm tree. Its filename is
mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch
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------------------------------------------------------
From: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
Subject: mlock: fix mlock count can not decrease in race condition
Kefeng reported that when running the follow test the mlock count in
meminfo cannot be decreased:
[1] testcase
linux:~ # cat test_mlockal
grep Mlocked /proc/meminfo
for j in `seq 0 10`
do
for i in `seq 4 15`
do
./p_mlockall >> log &
done
sleep 0.2
done
# wait some time to let mlock counter decrease and 5s may not enough
sleep 5
grep Mlocked /proc/meminfo
linux:~ # cat p_mlockall.c
#include <sys/mman.h>
#include <stdlib.h>
#include <stdio.h>
#define SPACE_LEN 4096
int main(int argc, char ** argv)
{
int ret;
void *adr = malloc(SPACE_LEN);
if (!adr)
return -1;
ret = mlockall(MCL_CURRENT | MCL_FUTURE);
printf("mlcokall ret = %d\n", ret);
ret = munlockall();
printf("munlcokall ret = %d\n", ret);
free(adr);
return 0;
}
In __munlock_pagevec() we ClearPageMlock but isolation_failed is in a race
condition, and we do not count these pages into delta_munlocked, which
causes the mlock counter to be incorrect for we cleared the PageMlock and
cannot count down the number in the future.
Fix it by countin the number of pages whose PageMlock flag is cleared.
Fixes: 1ebb7cc6a583 (" mm: munlock: batch NR_MLOCK zone state updates")
Link: http://lkml.kernel.org/r/1495678405-54569-1-git-send-email-xieyisheng1@xxxxxxxxxx
Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
Reported-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Tested-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Joern Engel <joern@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Xishi Qiu <qiuxishi@xxxxxxxxxx>
Cc: zhongjiang <zhongjiang@xxxxxxxxxx>
Cc: Hanjun Guo <guohanjun@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mlock.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN mm/mlock.c~mlock-fix-mlock-count-can-not-decrease-in-race-condition mm/mlock.c
--- a/mm/mlock.c~mlock-fix-mlock-count-can-not-decrease-in-race-condition
+++ a/mm/mlock.c
@@ -284,7 +284,7 @@ static void __munlock_pagevec(struct pag
{
int i;
int nr = pagevec_count(pvec);
- int delta_munlocked;
+ int delta_munlocked = -nr;
struct pagevec pvec_putback;
int pgrescued = 0;
@@ -304,6 +304,8 @@ static void __munlock_pagevec(struct pag
continue;
else
__munlock_isolation_failed(page);
+ } else {
+ delta_munlocked++;
}
/*
@@ -315,7 +317,6 @@ static void __munlock_pagevec(struct pag
pagevec_add(&pvec_putback, pvec->pages[i]);
pvec->pages[i] = NULL;
}
- delta_munlocked = -nr + pagevec_count(&pvec_putback);
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
spin_unlock_irq(zone_lru_lock(zone));
_
Patches currently in -mm which might be from xieyisheng1@xxxxxxxxxx are
mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch