This is a note to let you know that I've just added the patch titled
btrfs: Fix a deadlock in btrfs_dev_replace_finishing()
to the 3.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-a-deadlock-in-btrfs_dev_replace_finishing.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 12b894cb288d57292b01cf158177b6d5c89a6272 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Date: Wed, 20 Aug 2014 16:10:15 +0800
Subject: btrfs: Fix a deadlock in btrfs_dev_replace_finishing()
From: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
commit 12b894cb288d57292b01cf158177b6d5c89a6272 upstream.
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@xxxxxxxxxxxxxx>
Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
Cc: Stefan Behrens <sbehrens@xxxxxxxxxxxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/dev-replace.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -567,6 +567,8 @@ static int btrfs_dev_replace_finishing(s
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(s
* 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);
Patches currently in stable-queue which might be from quwenruo@xxxxxxxxxxxxxx are
queue-3.16/btrfs-fix-a-deadlock-in-btrfs_dev_replace_finishing.patch
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