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mm: find_get_pages_contig fixlet

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Testing ->mapping and ->index without a ref is not stable as the page
may have been reused at this point.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2011-01-13 15:45:51 -08:00 committed by Linus Torvalds
parent f0bc0a60b1
commit 9cbb4cb21b
1 changed files with 10 additions and 3 deletions
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13
mm/filemap.c
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@ -837,9 +837,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
if (radix_tree_deref_retry(page))
goto restart;
if (page->mapping == NULL || page->index != index)
break;
if (!page_cache_get_speculative(page))
goto repeat;
@ -849,6 +846,16 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
goto repeat;
}
/*
* must check mapping and index after taking the ref.
* otherwise we can get both false positives and false
* negatives, which is just confusing to the caller.
*/
if (page->mapping == NULL || page->index != index) {
page_cache_release(page);
break;
}
pages[ret] = page;
ret++;
index++;