On Tue, Apr 12, 2016 at 09:36:16PM +0800, Anand Jain wrote: > Move scratch super outside of the chunk lock to avoid below > lockdep warning. The better place to scratch super is in > the function btrfs_rm_dev_replace_free_srcdev() just before > free_device, which is outside of the chunk lock as well. > > To reproduce: > (fresh boot) > mkfs.btrfs -f -draid5 -mraid5 /dev/sdc /dev/sdd /dev/sde > mount /dev/sdc /btrfs > dd if=/dev/zero of=/btrfs/tf1 bs=4096 count=100 > (get devmgt from https://github.com/asj/devmgt.git) > devmgt detach /dev/sde > dd if=/dev/zero of=/btrfs/tf1 bs=4096 count=100 > sync > btrfs replace start -Brf 3 /dev/sdf /btrfs <-- > devmgt attach host7 > > ====================================================== > [ INFO: possible circular locking dependency detected ] > 4.6.0-rc2asj+ #1 Not tainted > --------------------------------------------------- > > btrfs/2174 is trying to acquire lock: > (sb_writers){.+.+.+}, at: > [<ffffffff812449b4>] __sb_start_write+0xb4/0xf0 > > but task is already holding lock: > (&fs_info->chunk_mutex){+.+.+.}, at: > [<ffffffffa05c5f55>] btrfs_dev_replace_finishing+0x145/0x980 [btrfs] > > which lock already depends on the new lock. > > Chain exists of: > sb_writers --> &fs_devs->device_list_mutex --> &fs_info->chunk_mutex > Possible unsafe locking scenario: > CPU0 CPU1 > ---- ---- > lock(&fs_info->chunk_mutex); > lock(&fs_devs->device_list_mutex); > lock(&fs_info->chunk_mutex); > lock(sb_writers); > > *** DEADLOCK *** > > -> #0 (sb_writers){.+.+.+}: > [<ffffffff810e6415>] __lock_acquire+0x1bc5/0x1ee0 > [<ffffffff810e707e>] lock_acquire+0xbe/0x210 > [<ffffffff810df49a>] percpu_down_read+0x4a/0xa0 > [<ffffffff812449b4>] __sb_start_write+0xb4/0xf0 > [<ffffffff81265534>] mnt_want_write+0x24/0x50 > [<ffffffff812508a2>] path_openat+0x952/0x1190 > [<ffffffff81252451>] do_filp_open+0x91/0x100 > [<ffffffff8123f5cc>] file_open_name+0xfc/0x140 > [<ffffffff8123f643>] filp_open+0x33/0x60 > [<ffffffffa0572bb6>] update_dev_time+0x16/0x40 [btrfs] > [<ffffffffa057f60d>] btrfs_scratch_superblocks+0x5d/0xb0 [btrfs] > [<ffffffffa057f70e>] btrfs_rm_dev_replace_remove_srcdev+0xae/0xd0 [btrfs] > [<ffffffffa05c62c5>] btrfs_dev_replace_finishing+0x4b5/0x980 [btrfs] > [<ffffffffa05c6ae8>] btrfs_dev_replace_start+0x358/0x530 [btrfs] > > Signed-off-by: Anand Jain <anand.j...@oracle.com>
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