btrfs: Fix a lockdep warning when running xfstest.

The following lockdep warning is triggered during xfstests:

[ 1702.980872] =========================================================
[ 1702.981181] [ INFO: possible irq lock inversion dependency detected ]
[ 1702.981482] 3.18.0-rc1 #27 Not tainted
[ 1702.981781] ---------------------------------------------------------
[ 1702.982095] kswapd0/77 just changed the state of lock:
[ 1702.982415]  (&delayed_node->mutex){+.+.-.}, at: [<ffffffffa03b0b51>] __btrfs_release_delayed_node+0x41/0x1f0 [btrfs]
[ 1702.982794] but this lock took another, RECLAIM_FS-unsafe lock in the past:
[ 1702.983160]  (&fs_info->dev_replace.lock){+.+.+.}

and interrupts could create inverse lock ordering between them.

[ 1702.984675]
other info that might help us debug this:
[ 1702.985524] Chain exists of:
  &delayed_node->mutex --> &found->groups_sem --> &fs_info->dev_replace.lock

[ 1702.986799]  Possible interrupt unsafe locking scenario:

[ 1702.987681]        CPU0                    CPU1
[ 1702.988137]        ----                    ----
[ 1702.988598]   lock(&fs_info->dev_replace.lock);
[ 1702.989069]                                local_irq_disable();
[ 1702.989534]                                lock(&delayed_node->mutex);
[ 1702.990038]                                lock(&found->groups_sem);
[ 1702.990494]   <Interrupt>
[ 1702.990938]     lock(&delayed_node->mutex);
[ 1702.991407]
 *** DEADLOCK ***

It is because the btrfs_kobj_{add/rm}_device() will call memory
allocation with GFP_KERNEL,
which may flush fs page cache to free space, waiting for it self to do
the commit, causing the deadlock.

To solve the problem, move btrfs_kobj_{add/rm}_device() out of the
dev_replace lock range, also involing split the
btrfs_rm_dev_replace_srcdev() function into remove and free parts.

Now only btrfs_rm_dev_replace_remove_srcdev() is called in dev_replace
lock range, and kobj_{add/rm} and btrfs_rm_dev_replace_free_srcdev() are
called out of the lock range.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d47289c715c8..01920515f90d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1800,8 +1800,8 @@ error_undo:
 	goto error_brelse;
 }
 
-void btrfs_rm_dev_replace_srcdev(struct btrfs_fs_info *fs_info,
-				 struct btrfs_device *srcdev)
+void btrfs_rm_dev_replace_remove_srcdev(struct btrfs_fs_info *fs_info,
+					struct btrfs_device *srcdev)
 {
 	struct btrfs_fs_devices *fs_devices;
 
@@ -1829,6 +1829,12 @@ void btrfs_rm_dev_replace_srcdev(struct btrfs_fs_info *fs_info,
 
 	if (srcdev->bdev)
 		fs_devices->open_devices--;
+}
+
+void btrfs_rm_dev_replace_free_srcdev(struct btrfs_fs_info *fs_info,
+				      struct btrfs_device *srcdev)
+{
+	struct btrfs_fs_devices *fs_devices = srcdev->fs_devices;
 
 	call_rcu(&srcdev->rcu, free_device);