• Yisheng Xie's avatar
    mlock: fix mlock count can not decrease in race condition · 70feee0e
    Yisheng Xie authored
    Kefeng reported that when running the follow test, the mlock count in
    meminfo will increase permanently:
    
     [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 should decrement NR_MLOCK for each page where
    we clear the PageMlocked flag.  Commit 1ebb7cc6 ("mm: munlock: batch
    NR_MLOCK zone state updates") has introduced a bug where we don't
    decrement NR_MLOCK for pages where we clear the flag, but fail to
    isolate them from the lru list (e.g.  when the pages are on some other
    cpu's percpu pagevec).  Since PageMlocked stays cleared, the NR_MLOCK
    accounting gets permanently disrupted by this.
    
    Fix it by counting the number of page whose PageMlock flag is cleared.
    
    Fixes: 1ebb7cc6 (" mm: munlock: batch NR_MLOCK zone state updates")
    Link: http://lkml.kernel.org/r/1495678405-54569-1-git-send-email-xieyisheng1@huawei.comSigned-off-by: 's avatarYisheng Xie <xieyisheng1@huawei.com>
    Reported-by: 's avatarKefeng Wang <wangkefeng.wang@huawei.com>
    Tested-by: 's avatarKefeng 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: Xishi Qiu <qiuxishi@huawei.com>
    Cc: zhongjiang <zhongjiang@huawei.com>
    Cc: Hanjun Guo <guohanjun@huawei.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    70feee0e
mlock.c 22.6 KB