+ mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch added to -mm tree

* + mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch added to -mm tree
@ 2017-05-24 22:04 akpm
  0 siblings, 0 replies; 3+ messages in thread
From: akpm @ 2017-05-24 22:04 UTC (permalink / raw)
  To: xieyisheng1, hannes, hughd, joern, mgorman, mhocko, riel, stable,
	vbabka, walken, wangkefeng.wang, mm-commits


The patch titled
     Subject: mm/mlock.c: 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@huawei.com>
Subject: mm/mlock.c: 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 in race
condition, and we do not count these page into delta_munlocked, which
causes mlock counter inaccuracy because we cleared the PageMlock and
cannot count down the number in the future.

Fix it by counting 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/1495620504-7007-1-git-send-email-xieyisheng1@huawei.com
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Joern Engel <joern@logfs.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mlock.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 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 munlocked = 0;
 	struct pagevec pvec_putback;
 	int pgrescued = 0;
 
@@ -296,6 +296,7 @@ static void __munlock_pagevec(struct pag
 		struct page *page = pvec->pages[i];
 
 		if (TestClearPageMlocked(page)) {
+			munlocked --;
 			/*
 			 * We already have pin from follow_page_mask()
 			 * so we can spare the get_page() here.
@@ -315,8 +316,8 @@ 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);
+	if (munlocked)
+		__mod_zone_page_state(zone, NR_MLOCK, munlocked);
 	spin_unlock_irq(zone_lru_lock(zone));
 
 	/* Now we can release pins of pages that we are not munlocking */
_

Patches currently in -mm which might be from xieyisheng1@huawei.com are

mlock-fix-mlock-count-can-not-decrease-in-race-condition.patch


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