3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Josef Bacik jbacik@fb.com
commit 3c4276936f6fbe52884b4ea4e6cc120b890a0f9f upstream.
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.
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 [bwh: Backported to 3.16: deleted function is slightly different] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5542,31 +5542,6 @@ err: 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(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, root); - } - 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. --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -1852,7 +1852,6 @@ static const struct super_operations btr .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,