| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.17 003/146] btrfs: Fix a deadlock in btrfs_dev_replace_finishing() | Date | Tue, 28 Oct 2014 11:32:25 +0800 |
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3.17-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo <quwenruo@cn.fujitsu.com>
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@cn.fujitsu.com> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Cc: Stefan Behrens <sbehrens@giantdisaster.de> Signed-off-by: Chris Mason <clm@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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);
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