diff options
author | Hugh Dickins <hughd@google.com> | 2012-10-08 16:33:19 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-09 16:22:56 +0900 |
commit | e6c509f85455041d3d7c4b863bf80bc294288cc1 (patch) | |
tree | 50ccf8e339b219851ca7ad000379b1559415e354 /mm/mlock.c | |
parent | 39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff) | |
download | op-kernel-dev-e6c509f85455041d3d7c4b863bf80bc294288cc1.zip op-kernel-dev-e6c509f85455041d3d7c4b863bf80bc294288cc1.tar.gz |
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/mlock.c')
-rw-r--r-- | mm/mlock.c | 16 |
1 files changed, 3 insertions, 13 deletions
@@ -51,13 +51,10 @@ EXPORT_SYMBOL(can_do_mlock); /* * LRU accounting for clear_page_mlock() */ -void __clear_page_mlock(struct page *page) +void clear_page_mlock(struct page *page) { - VM_BUG_ON(!PageLocked(page)); - - if (!page->mapping) { /* truncated ? */ + if (!TestClearPageMlocked(page)) return; - } dec_zone_page_state(page, NR_MLOCK); count_vm_event(UNEVICTABLE_PGCLEARED); @@ -290,14 +287,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma, page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); if (page && !IS_ERR(page)) { lock_page(page); - /* - * Like in __mlock_vma_pages_range(), - * because we lock page here and migration is - * blocked by the elevated reference, we need - * only check for file-cache page truncation. - */ - if (page->mapping) - munlock_vma_page(page); + munlock_vma_page(page); unlock_page(page); put_page(page); } |