From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miao Xie Subject: [RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare interface Date: Thu, 22 Mar 2012 11:13:17 +0800 Message-ID: <4F6A98CD.5090701@cn.fujitsu.com> Reply-To: miaox@cn.fujitsu.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Linux Btrfs , Linux Fsdevel To: Chris Mason , viro Return-path: List-ID: The reason the deadlock is that: Task Btrfs-cleaner umount() down_write(&s->s_umount) close_ctree() wait for the end of btrfs-cleaner start_transaction reserve space shrink_delalloc() writeback_inodes_sb_nr_if_idle() down_read(&sb->s_umount) So, the deadlock has happened. The safest way to fix this problem is to close the btrfs-cleaner before the umount is ready to continue. Since we have introduced umount_prepare interface into vfs before, we can fix this problem by it. Reported-by: Tsutomu Itoh Signed-off-by: Miao Xie --- fs/btrfs/disk-io.c | 15 --------------- fs/btrfs/super.c | 22 ++++++++++++++++++++++ 2 files changed, 22 insertions(+), 15 deletions(-) diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 534266f..34ebd6e 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -3017,21 +3017,6 @@ int close_ctree(struct btrfs_root *root) struct btrfs_fs_info *fs_info = root->fs_info; int ret; - fs_info->closing = 1; - smp_mb(); - - /* pause restriper - we want to resume on mount */ - btrfs_pause_balance(root->fs_info); - - btrfs_scrub_cancel(root); - - /* wait for any defraggers to finish */ - wait_event(fs_info->transaction_wait, - (atomic_read(&fs_info->defrag_running) == 0)); - - /* clear out the rbtree of defraggable inodes */ - btrfs_run_defrag_inodes(fs_info); - /* * Here come 2 situations when btrfs is broken to flip readonly: * diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index 3ce97b2..24ed903 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -145,6 +145,27 @@ void __btrfs_std_error(struct btrfs_fs_info *fs_info, const char *function, btrfs_handle_error(fs_info); } +static void btrfs_umount_prepare(struct super_block *sb) +{ + struct btrfs_root *root = btrfs_sb(sb)->tree_root; + struct btrfs_fs_info *fs_info = root->fs_info; + + fs_info->closing = 1; + smp_mb(); + + /* pause restriper - we want to resume on mount */ + btrfs_pause_balance(root->fs_info); + + btrfs_scrub_cancel(root); + + /* wait for any defraggers to finish */ + wait_event(fs_info->transaction_wait, + (atomic_read(&fs_info->defrag_running) == 0)); + + /* clear out the rbtree of defraggable inodes */ + btrfs_run_defrag_inodes(fs_info); +} + static void btrfs_put_super(struct super_block *sb) { (void)close_ctree(btrfs_sb(sb)->tree_root); @@ -1312,6 +1333,7 @@ static void btrfs_fs_dirty_inode(struct inode *inode, int flags) static const struct super_operations btrfs_super_ops = { .drop_inode = btrfs_drop_inode, .evict_inode = btrfs_evict_inode, + .umount_prepare = btrfs_umount_prepare, .put_super = btrfs_put_super, .sync_fs = btrfs_sync_fs, .show_options = btrfs_show_options, -- 1.7.6.5