From: Joe Thornber <ejt@redhat.com>
Date: Thu, 11 Jun 2015 16:11:48 +0000 (+0100)
Subject: dm thin metadata: fix a race when entering fail mode
X-Git-Tag: v4.2-rc1~112^2~6
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b1f11aff04cc86daa0757ada5deb669a92a8f0fb;p=karo-tx-linux.git

dm thin metadata: fix a race when entering fail mode

In dm_thin_find_block() the ->fail_io flag was checked outside the
metadata device's root_lock, causing dm_thin_find_block() to race with
the setting of this flag.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 8b521e3e1e1b..48dfe3c4d6aa 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1390,10 +1390,11 @@ int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
 	dm_block_t keys[2] = { td->id, block };
 	struct dm_btree_info *info;
 
-	if (pmd->fail_io)
-		return -EINVAL;
-
 	down_read(&pmd->root_lock);
+	if (pmd->fail_io) {
+		up_read(&pmd->root_lock);
+		return -EINVAL;
+	}
 
 	if (can_issue_io) {
 		info = &pmd->info;