[ 25/44] drivers/block/brd.c: fix brd_lookup_page() race

From: Greg Kroah-Hartman
Date: Wed Jun 05 2013 - 17:16:28 EST

3.4-stable review patch. If anyone has any objections, please let me know.


From: Brian Behlendorf <behlendorf1@xxxxxxxx>

commit dfd20b2b174d3a9b258ea3b7a35ead33576587b1 upstream.

The index on the page must be set before it is inserted in the radix
tree. Otherwise there is a small race which can occur during lookup
where the page can be found with the incorrect index. This will trigger
the BUG_ON() in brd_lookup_page().

Signed-off-by: Brian Behlendorf <behlendorf1@xxxxxxxx>
Reported-by: Chris Wedgwood <cw@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/block/brd.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -117,13 +117,13 @@ static struct page *brd_insert_page(stru

idx = sector >> PAGE_SECTORS_SHIFT;
+ page->index = idx;
if (radix_tree_insert(&brd->brd_pages, idx, page)) {
page = radix_tree_lookup(&brd->brd_pages, idx);
BUG_ON(page->index != idx);
- } else
- page->index = idx;
+ }


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