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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/mlock.c
parent39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff)
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.c16
1 files changed, 3 insertions, 13 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index a948be4b7ba7..de7321592897 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -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);
}