[ 3.8.y.z extended stable ] Patch "drivers/block/brd.c: fix brd_lookup_page() race" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    drivers/block/brd.c: fix brd_lookup_page() race

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 92b12b6abad953b7882c777af51a5d5445683bc9 Mon Sep 17 00:00:00 2001
From: Brian Behlendorf <behlendorf1 at llnl.gov>
Date: Fri, 24 May 2013 15:55:28 -0700
Subject: drivers/block/brd.c: fix brd_lookup_page() race

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 at llnl.gov>
Reported-by: Chris Wedgwood <cw at f00f.org>
Cc: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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();
--
1.8.1.2