Qu Wenruo
2014-Aug-20 08:10 UTC
[PATCH] btrfs: Fix a deadlock in btrfs_dev_replace_finishing()
btrfs-transacion:5657
[stack snip]
btrfs_bio_map()
btrfs_bio_counter_inc_blocked()
percpu_counter_inc(&fs_info->bio_counter) ###bio_counter >
0(A)
__btrfs_bio_map()
btrfs_dev_replace_lock()
mutex_lock(dev_replace->lock) ###wait mutex(B)
btrfs:32612
[stack snip]
btrfs_dev_replace_start()
btrfs_dev_replace_lock()
mutex_lock(dev_replace->lock) ###hold mutex(B)
btrfs_dev_replace_finishing()
btrfs_rm_dev_replace_blocked()
wait until percpu_counter_sum == 0 ###wait on bio_counter(A)
This bug can be triggered quite easily by the following test script:
http://pastebin.com/MQmb37Cy
This patch will fix the ABBA problem by calling
btrfs_dev_replace_unlock() before btrfs_rm_dev_replace_blocked().
The consistency of btrfs devices list and their superblocks is protected
by device_list_mutex, not btrfs_dev_replace_lock/unlock().
So it is safe the move btrfs_dev_replace_unlock() before
btrfs_rm_dev_replace_blocked().
Reported-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Cc: Stefan Behrens <sbehrens@giantdisaster.de>
---
fs/btrfs/dev-replace.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index eea26e1..d738ff8 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -567,6 +567,8 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info
*fs_info,
btrfs_kobj_rm_device(fs_info, src_device);
btrfs_kobj_add_device(fs_info, tgt_device);
+ btrfs_dev_replace_unlock(dev_replace);
+
btrfs_rm_dev_replace_blocked(fs_info);
btrfs_rm_dev_replace_srcdev(fs_info, src_device);
@@ -580,7 +582,6 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info
*fs_info,
* superblock is scratched out so that it is no longer marked to
* belong to this filesystem.
*/
- btrfs_dev_replace_unlock(dev_replace);
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
mutex_unlock(&root->fs_info->chunk_mutex);
--
2.0.4
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