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author | Hugh Dickins <hughd@google.com> | 2012-10-08 16:33:19 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-09 16:22:56 +0900 |
commit | e6c509f85455041d3d7c4b863bf80bc294288cc1 (patch) | |
tree | 50ccf8e339b219851ca7ad000379b1559415e354 /mm/internal.h | |
parent | 39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff) | |
download | lwn-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/internal.h')
-rw-r--r-- | mm/internal.h | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/mm/internal.h b/mm/internal.h index 78f25d6cc6a7..4dc93e2fe69e 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -201,12 +201,7 @@ extern void munlock_vma_page(struct page *page); * If called for a page that is still mapped by mlocked vmas, all we do * is revert to lazy LRU behaviour -- semantics are not broken. */ -extern void __clear_page_mlock(struct page *page); -static inline void clear_page_mlock(struct page *page) -{ - if (unlikely(TestClearPageMlocked(page))) - __clear_page_mlock(page); -} +extern void clear_page_mlock(struct page *page); /* * mlock_migrate_page - called only from migrate_page_copy() to |