btrfs_map_bio() first calls btrfs_bio_counter_inc_blocked() which checks
fs state and increase bio_counter, then calls __btrfs_map_block() which
will take the dev_replace lock.
On the other hand, btrfs_dev_replace_finishing() takes dev_replace lock
first then set fs state to BTRFS_FS_STATE_DEV_REPLACING and waits for
bio_counter to be zero.
The deadlock can be reproduced easily by running replace and fsstress at
the same time, e.g.
mkfs -t btrfs -f /dev/sdb1 /dev/sdb2
mount /dev/sdb1 /mnt/btrfs
fsstress -d /mnt/btrfs -n 100 -p 2 -l 0 & # fsstress from ltp supports -l option
i=0
while btrfs replace start -Bf /dev/sdb2 /dev/sdb3 /mnt/btrfs && \
btrfs replace start -Bf /dev/sdb3 /dev/sdb2 /mnt/btrfs; do
echo "=== loop $i ==="
let i=$i+1
done
This was introduced by
c404e0d Btrfs: fix use-after-free in the finishing procedure of the device
replace
Signed-off-by: Eryu Guan <guane...@gmail.com>
---
Tested by the reproducer and xfstests, no new failure found.
But I found kmem_cache leak if I remove btrfs module after my new test case[1],
which does fsstress & replace & subvolume create/mount/umount/delete at the same
time.
BUG btrfs_extent_state (Tainted: G B ): Objects remaining in
btrfs_extent_state on kmem_cache_close()
......
kmem_cache_destroy btrfs_extent_state: Slab cache still has objects
CPU: 3 PID: 9503 Comm: modprobe Tainted: G B 3.17.0-rc5+ #12
Hardware name: Hewlett-Packard ProLiant DL388eGen8, BIOS P73 06/01/2012
0000000000000000 000000008dd09c52 ffff880411c37eb0 ffffffff81642f7a
ffff8800b9a19300 ffff880411c37ed0 ffffffff8118ce89 0000000000000000
ffffffffa05dcd20 ffff880411c37ee0 ffffffffa056a80f ffff880411c37ef0
Call Trace:
[<ffffffff81642f7a>] dump_stack+0x45/0x56
[<ffffffff8118ce89>] kmem_cache_destroy+0xf9/0x100
[<ffffffffa056a80f>] extent_io_exit+0x1f/0x50 [btrfs]
[<ffffffffa05c3ae3>] exit_btrfs_fs+0x2c/0x549 [btrfs]
[<ffffffff810efda2>] SyS_delete_module+0x162/0x200
[<ffffffff81013bb7>] ? do_notify_resume+0x97/0xb0
[<ffffffff8164af69>] system_call_fastpath+0x16/0x1b
The test would hang before the fix. I'm not sure if it's related to the fix
(seems not), please help review.
Thanks,
Eryu Guan
[1] http://www.spinics.net/lists/linux-btrfs/msg37625.html
fs/btrfs/dev-replace.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index eea26e1..5dfd292 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -510,6 +510,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info
*fs_info,
/* keep away write_all_supers() during the finishing procedure */
mutex_lock(&root->fs_info->chunk_mutex);
mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
+ btrfs_rm_dev_replace_blocked(fs_info);
btrfs_dev_replace_lock(dev_replace);
dev_replace->replace_state =
scrub_ret ? BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED
@@ -567,12 +568,8 @@ 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_rm_dev_replace_blocked(fs_info);
-
btrfs_rm_dev_replace_srcdev(fs_info, src_device);
- btrfs_rm_dev_replace_unblocked(fs_info);
-
/*
* this is again a consistent state where no dev_replace procedure
* is running, the target device is part of the filesystem, the
@@ -581,6 +578,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info
*fs_info,
* belong to this filesystem.
*/
btrfs_dev_replace_unlock(dev_replace);
+ btrfs_rm_dev_replace_unblocked(fs_info);
mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
mutex_unlock(&root->fs_info->chunk_mutex);
--
1.8.3.1
--
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