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 8b521e3e1e1b91e90e1821ddf70c37dd55a09d85..48dfe3c4d6aa7968bbc1986eafcb9e965fe55950 100644 (file)
--- 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;