[030/141] drivers/block/brd.c: fix brd_lookup_page() race

Steven Rostedt
2013-07-03T18:52:40Z

[-- Attachment #1: 0030-drivers-block-brd.c-fix-brd_lookup_page-race.patch --]
[-- Type: text/plain, Size: 1488 bytes --]

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

------------------

From: Brian Behlendorf <behlendorf1@llnl.gov>

[ Upstream commit dfd20b2b174d3a9b258ea3b7a35ead33576587b1 ]

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@llnl.gov>
Reported-by: Chris Wedgwood <cw@f00f.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
drivers/block/brd.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 531ceb3..4e8213a 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -117,13 +117,13 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)

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

radix_tree_preload_end();
--
1.7.10.4