linux-kernel - [65/94] drivers/block/brd.c: fix brd_lookup

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Message-ID: <lsq.1369712993.153895933@decadent.org.uk>
Date:	Tue, 28 May 2013 04:49:53 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Jens Axboe" <axboe@...nel.dk>,
	"Brian Behlendorf" <behlendorf1@...l.gov>,
	"Chris Wedgwood" <cw@...f.org>
Subject: [65/94] drivers/block/brd.c: fix brd_lookup_page() race

3.2.46-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Brian Behlendorf <behlendorf1@...l.gov>

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@...l.gov>
Reported-by: Chris Wedgwood <cw@...f.org>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
 
 	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();

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