From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org Subject: [PATCH 4.5 118/128] btrfs: fix lock dep warning move scratch super outside of chunk_mutex Date: Sun, 5 Jun 2016 15:24:33 -0700 Message-Id: <20160605222324.981705825@linuxfoundation.org> In-Reply-To: <20160605222321.183131188@linuxfoundation.org> References: <20160605222321.183131188@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Anand Jain commit 48b3b9d401ec86899a52003b37331190a35a81a6 upstream. 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: [] __sb_start_write+0xb4/0xf0 but task is already holding lock: (&fs_info->chunk_mutex){+.+.+.}, at: [] 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); --- fs/btrfs/volumes.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1971,11 +1971,8 @@ void btrfs_rm_dev_replace_remove_srcdev( if (srcdev->missing) fs_devices->missing_devices--; - if (srcdev->writeable) { + if (srcdev->writeable) fs_devices->rw_devices--; - /* zero out the old super if it is writable */ - btrfs_scratch_superblocks(srcdev->bdev, srcdev->name->str); - } if (srcdev->bdev) fs_devices->open_devices--; @@ -1986,6 +1983,10 @@ void btrfs_rm_dev_replace_free_srcdev(st { struct btrfs_fs_devices *fs_devices = srcdev->fs_devices; + if (srcdev->writeable) { + /* zero out the old super if it is writable */ + btrfs_scratch_superblocks(srcdev->bdev, srcdev->name->str); + } call_rcu(&srcdev->rcu, free_device); /*