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Btrfs: fix btrfs_write_inode vs delayed iput deadlock

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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 4730a4bc5b
("btrfs_dirty_inode") to support O_SYNC writes. However, ->write_inode()
hasn't been used for O_SYNC since 148f948ba8 ("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>
This commit is contained in:
Josef Bacik 2018-07-20 11:46:10 -07:00 committed by David Sterba
parent 97aff912a2
commit 3c4276936f
2 changed files with 0 additions and 27 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

26
fs/btrfs/inode.c
View file

@ -6021,32 +6021,6 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
return ret; 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 * This is somewhat expensive, updating the tree every time the
* inode changes. But, it is most likely to find the inode in cache. * inode changes. But, it is most likely to find the inode in cache.

1
fs/btrfs/super.c
View file

@ -2344,7 +2344,6 @@ static const struct super_operations btrfs_super_ops = {
.sync_fs = btrfs_sync_fs, .sync_fs = btrfs_sync_fs,
.show_options = btrfs_show_options, .show_options = btrfs_show_options,
.show_devname = btrfs_show_devname, .show_devname = btrfs_show_devname,
.write_inode = btrfs_write_inode,
.alloc_inode = btrfs_alloc_inode, .alloc_inode = btrfs_alloc_inode,
.destroy_inode = btrfs_destroy_inode, .destroy_inode = btrfs_destroy_inode,
.statfs = btrfs_statfs, .statfs = btrfs_statfs,