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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
parent39b5f29ac1f988c1615fbc9c69f6651ab0d0c3c7 (diff)
downloadlinux-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')
-rw-r--r--mm/internal.h7
-rw-r--r--mm/memory.c10
-rw-r--r--mm/mlock.c16
-rw-r--r--mm/rmap.c4
-rw-r--r--mm/truncate.c4
5 files changed, 13 insertions, 28 deletions
diff --git a/mm/internal.h b/mm/internal.h
index 78f25d6cc6a..4dc93e2fe69 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
diff --git a/mm/memory.c b/mm/memory.c
index d205e4381a3..5f5d1f039bf 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1577,12 +1577,12 @@ split_fallthrough:
if (page->mapping && trylock_page(page)) {
lru_add_drain(); /* push cached pages to LRU */
/*
- * Because we lock page here and migration is
- * blocked by the pte's page reference, we need
- * only check for file-cache page truncation.
+ * Because we lock page here, and migration is
+ * blocked by the pte's page reference, and we
+ * know the page is still mapped, we don't even
+ * need to check for file-cache page truncation.
*/
- if (page->mapping)
- mlock_vma_page(page);
+ mlock_vma_page(page);
unlock_page(page);
}
}
diff --git a/mm/mlock.c b/mm/mlock.c
index a948be4b7ba..de732159289 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);
}
diff --git a/mm/rmap.c b/mm/rmap.c
index 0d86433e42d..bf03149f495 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);
diff --git a/mm/truncate.c b/mm/truncate.c
index f38055cb8af..d51ce92d6e8 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -107,7 +107,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
cancel_dirty_page(page, PAGE_CACHE_SIZE);
- clear_page_mlock(page);
ClearPageMappedToDisk(page);
delete_from_page_cache(page);
return 0;
@@ -132,7 +131,6 @@ invalidate_complete_page(struct address_space *mapping, struct page *page)
if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;
- clear_page_mlock(page);
ret = remove_mapping(mapping, page);
return ret;
@@ -394,8 +392,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
- clear_page_mlock(page);
-
spin_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;