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authorHugh Dickins <hughd@google.com>2012-10-08 16:33:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:56 +0900
commite6c509f85455041d3d7c4b863bf80bc294288cc1 (patch)
tree50ccf8e339b219851ca7ad000379b1559415e354 /mm/rmap.c
parent39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff)
downloadlwn-e6c509f85455041d3d7c4b863bf80bc294288cc1.tar.gz
lwn-e6c509f85455041d3d7c4b863bf80bc294288cc1.zip
mm: use clear_page_mlock() in page_remove_rmap()
We had thought that pages could no longer get freed while still marked as mlocked; but Johannes Weiner posted this program to demonstrate that truncating an mlocked private file mapping containing COWed pages is still mishandled: #include <sys/types.h> #include <sys/mman.h> #include <sys/stat.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <stdio.h> int main(void) { char *map; int fd; system("grep mlockfreed /proc/vmstat"); fd = open("chigurh", O_CREAT|O_EXCL|O_RDWR); unlink("chigurh"); ftruncate(fd, 4096); map = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE, fd, 0); map[0] = 11; mlock(map, sizeof(fd)); ftruncate(fd, 0); close(fd); munlock(map, sizeof(fd)); munmap(map, 4096); system("grep mlockfreed /proc/vmstat"); return 0; } The anon COWed pages are not caught by truncation's clear_page_mlock() of the pagecache pages; but unmap_mapping_range() unmaps them, so we ought to look out for them there in page_remove_rmap(). Indeed, why should truncation or invalidation be doing the clear_page_mlock() when removing from pagecache? mlock is a property of mapping in userspace, not a property of pagecache: an mlocked unmapped page is nonsensical. Reported-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Rik van Riel <riel@redhat.com> Cc: Michel Lespinasse <walken@google.com> Cc: Ying Han <yinghan@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
-rw-r--r--mm/rmap.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index 0d86433e42d7..bf03149f495c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1155,7 +1155,10 @@ void page_remove_rmap(struct page *page)
} else {
__dec_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
+ mem_cgroup_end_update_page_stat(page, &locked, &flags);
}
+ if (unlikely(PageMlocked(page)))
+ clear_page_mlock(page);
/*
* It would be tidy to reset the PageAnon mapping here,
* but that might overwrite a racing page_add_anon_rmap
@@ -1165,6 +1168,7 @@ void page_remove_rmap(struct page *page)
* Leaving it set also helps swapoff to reinstate ptes
* faster for those pages still in swapcache.
*/
+ return;
out:
if (!anon)
mem_cgroup_end_update_page_stat(page, &locked, &flags);