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    btrfs: fix lock dep warning move scratch super outside of chunk_mutex · 48b3b9d4
    Anand Jain 提交于
    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: NAnand Jain <anand.jain@oracle.com>
    Signed-off-by: NDavid Sterba <dsterba@suse.com>
    48b3b9d4
volumes.c 183.5 KB