The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3c4276936f6fbe52884b4ea4e6cc120b890a0f9f Mon Sep 17 00:00:00 2001

From: Josef Bacik jbacik@fb.com Date: Fri, 20 Jul 2018 11:46:10 -0700 Subject: [PATCH] Btrfs: fix btrfs_write_inode vs delayed iput deadlock

We recently ran into the following deadlock involving btrfs_write_inode():

[ +0.005066] __schedule+0x38e/0x8c0 [ +0.007144] schedule+0x36/0x80 [ +0.006447] bit_wait+0x11/0x60 [ +0.006446] __wait_on_bit+0xbe/0x110 [ +0.007487] ? bit_wait_io+0x60/0x60 [ +0.007319] __inode_wait_for_writeback+0x96/0xc0 [ +0.009568] ? autoremove_wake_function+0x40/0x40 [ +0.009565] inode_wait_for_writeback+0x21/0x30 [ +0.009224] evict+0xb0/0x190 [ +0.006099] iput+0x1a8/0x210 [ +0.006103] btrfs_run_delayed_iputs+0x73/0xc0 [ +0.009047] btrfs_commit_transaction+0x799/0x8c0 [ +0.009567] btrfs_write_inode+0x81/0xb0 [ +0.008008] __writeback_single_inode+0x267/0x320 [ +0.009569] writeback_sb_inodes+0x25b/0x4e0 [ +0.008702] wb_writeback+0x102/0x2d0 [ +0.007487] wb_workfn+0xa4/0x310 [ +0.006794] ? wb_workfn+0xa4/0x310 [ +0.007143] process_one_work+0x150/0x410 [ +0.008179] worker_thread+0x6d/0x520 [ +0.007490] kthread+0x12c/0x160 [ +0.006620] ? put_pwq_unlocked+0x80/0x80 [ +0.008185] ? kthread_park+0xa0/0xa0 [ +0.007484] ? do_syscall_64+0x53/0x150 [ +0.007837] ret_from_fork+0x29/0x40

Writeback calls:

btrfs_write_inode btrfs_commit_transaction btrfs_run_delayed_iputs

If iput() is called on that same inode, evict() will wait for writeback forever.

btrfs_write_inode() was originally added way back in 4730a4bc5bf3 ("btrfs_dirty_inode") to support O_SYNC writes. However, ->write_inode() hasn't been used for O_SYNC since 148f948ba877 ("vfs: Introduce new helpers for syncing after writing to O_SYNC file or IS_SYNC inode"), so btrfs_write_inode() is actually unnecessary (and leads to a bunch of unnecessary commits). Get rid of it, which also gets rid of the deadlock.

CC: stable@vger.kernel.org # 3.2+ Signed-off-by: Josef Bacik jbacik@fb.com [Omar: new commit message] Signed-off-by: Omar Sandoval osandov@fb.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 4955e04da4c8..472457795486 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -6021,32 +6021,6 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx) return ret; }

-int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc) -{ - struct btrfs_root *root = BTRFS_I(inode)->root; - struct btrfs_trans_handle *trans; - int ret = 0; - bool nolock = false; - - if (test_bit(BTRFS_INODE_DUMMY, &BTRFS_I(inode)->runtime_flags)) - return 0; - - if (btrfs_fs_closing(root->fs_info) && - btrfs_is_free_space_inode(BTRFS_I(inode))) - nolock = true; - - if (wbc->sync_mode == WB_SYNC_ALL) { - if (nolock) - trans = btrfs_join_transaction_nolock(root); - else - trans = btrfs_join_transaction(root); - if (IS_ERR(trans)) - return PTR_ERR(trans); - ret = btrfs_commit_transaction(trans); - } - return ret; -} - /* * This is somewhat expensive, updating the tree every time the * inode changes. But, it is most likely to find the inode in cache. diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index efe8b03ce380..67de3c0fc85b 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -2344,7 +2344,6 @@ static const struct super_operations btrfs_super_ops = { .sync_fs = btrfs_sync_fs, .show_options = btrfs_show_options, .show_devname = btrfs_show_devname, - .write_inode = btrfs_write_inode, .alloc_inode = btrfs_alloc_inode, .destroy_inode = btrfs_destroy_inode, .statfs = btrfs_statfs,