Qu Wenruo
2014-Oct-30 08:52 UTC
[PATCH] 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>
---
fs/btrfs/dev-replace.c | 11 ++++++-----
fs/btrfs/volumes.c | 10 ++++++++--
fs/btrfs/volumes.h | 6 ++++--
3 files changed, 18 insertions(+), 9 deletions(-)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 6f662b3..6e3e885 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -571,15 +571,11 @@ static int btrfs_dev_replace_finishing(struct
btrfs_fs_info *fs_info,
list_add(&tgt_device->dev_alloc_list,
&fs_info->fs_devices->alloc_list);
fs_info->fs_devices->rw_devices++;
- /* replace the sysfs entry */
- 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);
+ btrfs_rm_dev_replace_remove_srcdev(fs_info, src_device);
btrfs_rm_dev_replace_unblocked(fs_info);
@@ -594,6 +590,11 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info
*fs_info,
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
mutex_unlock(&uuid_mutex);
+ /* replace the sysfs entry */
+ btrfs_kobj_rm_device(fs_info, src_device);
+ btrfs_kobj_add_device(fs_info, tgt_device);
+ btrfs_rm_dev_replace_free_srcdev(fs_info, src_device);
+
/* write back the superblocks */
trans = btrfs_start_transaction(root, 0);
if (!IS_ERR(trans))
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d47289c..0192051 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);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 08980fa..4cc00e6 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -448,8 +448,10 @@ void btrfs_init_devices_late(struct btrfs_fs_info
*fs_info);
int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info);
int btrfs_run_dev_stats(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info);
-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);
+void btrfs_rm_dev_replace_free_srcdev(struct btrfs_fs_info *fs_info,
+ struct btrfs_device *srcdev);
void btrfs_destroy_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
struct btrfs_device *tgtdev);
void btrfs_init_dev_replace_tgtdev_for_resume(struct btrfs_fs_info *fs_info,
--
2.1.2
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