tree 87a24920f29b2b701e8196c71797200572581692
parent 626e9f41f7c281ba3e02843702f68471706aa6d9
author Filipe Manana <fdmanana@suse.com> 1619089685 +0100
committer David Sterba <dsterba@suse.com> 1619633387 +0200

btrfs: fix deadlock when cloning inline extents and using qgroups

There are a few exceptional cases where cloning an inline extent needs to
copy the inline extent data into a page of the destination inode.

When this happens, we end up starting a transaction while having a dirty
page for the destination inode and while having the range locked in the
destination's inode iotree too. Because when reserving metadata space
for a transaction we may need to flush existing delalloc in case there is
not enough free space, we have a mechanism in place to prevent a deadlock,
which was introduced in commit 3d45f221ce627d ("btrfs: fix deadlock when
cloning inline extent and low on free metadata space").

However when using qgroups, a transaction also reserves metadata qgroup
space, which can also result in flushing delalloc in case there is not
enough available space at the moment. When this happens we deadlock, since
flushing delalloc requires locking the file range in the inode's iotree
and the range was already locked at the very beginning of the clone
operation, before attempting to start the transaction.

When this issue happens, stack traces like the following are reported:

  [72747.556262] task:kworker/u81:9   state:D stack:    0 pid:  225 ppid:     2 flags:0x00004000
  [72747.556268] Workqueue: writeback wb_workfn (flush-btrfs-1142)
  [72747.556271] Call Trace:
  [72747.556273]  __schedule+0x296/0x760
  [72747.556277]  schedule+0x3c/0xa0
  [72747.556279]  io_schedule+0x12/0x40
  [72747.556284]  __lock_page+0x13c/0x280
  [72747.556287]  ? generic_file_readonly_mmap+0x70/0x70
  [72747.556325]  extent_write_cache_pages+0x22a/0x440 [btrfs]
  [72747.556331]  ? __set_page_dirty_nobuffers+0xe7/0x160
  [72747.556358]  ? set_extent_buffer_dirty+0x5e/0x80 [btrfs]
  [72747.556362]  ? update_group_capacity+0x25/0x210
  [72747.556366]  ? cpumask_next_and+0x1a/0x20
  [72747.556391]  extent_writepages+0x44/0xa0 [btrfs]
  [72747.556394]  do_writepages+0x41/0xd0
  [72747.556398]  __writeback_single_inode+0x39/0x2a0
  [72747.556403]  writeback_sb_inodes+0x1ea/0x440
  [72747.556407]  __writeback_inodes_wb+0x5f/0xc0
  [72747.556410]  wb_writeback+0x235/0x2b0
  [72747.556414]  ? get_nr_inodes+0x35/0x50
  [72747.556417]  wb_workfn+0x354/0x490
  [72747.556420]  ? newidle_balance+0x2c5/0x3e0
  [72747.556424]  process_one_work+0x1aa/0x340
  [72747.556426]  worker_thread+0x30/0x390
  [72747.556429]  ? create_worker+0x1a0/0x1a0
  [72747.556432]  kthread+0x116/0x130
  [72747.556435]  ? kthread_park+0x80/0x80
  [72747.556438]  ret_from_fork+0x1f/0x30

  [72747.566958] Workqueue: btrfs-flush_delalloc btrfs_work_helper [btrfs]
  [72747.566961] Call Trace:
  [72747.566964]  __schedule+0x296/0x760
  [72747.566968]  ? finish_wait+0x80/0x80
  [72747.566970]  schedule+0x3c/0xa0
  [72747.566995]  wait_extent_bit.constprop.68+0x13b/0x1c0 [btrfs]
  [72747.566999]  ? finish_wait+0x80/0x80
  [72747.567024]  lock_extent_bits+0x37/0x90 [btrfs]
  [72747.567047]  btrfs_invalidatepage+0x299/0x2c0 [btrfs]
  [72747.567051]  ? find_get_pages_range_tag+0x2cd/0x380
  [72747.567076]  __extent_writepage+0x203/0x320 [btrfs]
  [72747.567102]  extent_write_cache_pages+0x2bb/0x440 [btrfs]
  [72747.567106]  ? update_load_avg+0x7e/0x5f0
  [72747.567109]  ? enqueue_entity+0xf4/0x6f0
  [72747.567134]  extent_writepages+0x44/0xa0 [btrfs]
  [72747.567137]  ? enqueue_task_fair+0x93/0x6f0
  [72747.567140]  do_writepages+0x41/0xd0
  [72747.567144]  __filemap_fdatawrite_range+0xc7/0x100
  [72747.567167]  btrfs_run_delalloc_work+0x17/0x40 [btrfs]
  [72747.567195]  btrfs_work_helper+0xc2/0x300 [btrfs]
  [72747.567200]  process_one_work+0x1aa/0x340
  [72747.567202]  worker_thread+0x30/0x390
  [72747.567205]  ? create_worker+0x1a0/0x1a0
  [72747.567208]  kthread+0x116/0x130
  [72747.567211]  ? kthread_park+0x80/0x80
  [72747.567214]  ret_from_fork+0x1f/0x30

  [72747.569686] task:fsstress        state:D stack:    0 pid:841421 ppid:841417 flags:0x00000000
  [72747.569689] Call Trace:
  [72747.569691]  __schedule+0x296/0x760
  [72747.569694]  schedule+0x3c/0xa0
  [72747.569721]  try_flush_qgroup+0x95/0x140 [btrfs]
  [72747.569725]  ? finish_wait+0x80/0x80
  [72747.569753]  btrfs_qgroup_reserve_data+0x34/0x50 [btrfs]
  [72747.569781]  btrfs_check_data_free_space+0x5f/0xa0 [btrfs]
  [72747.569804]  btrfs_buffered_write+0x1f7/0x7f0 [btrfs]
  [72747.569810]  ? path_lookupat.isra.48+0x97/0x140
  [72747.569833]  btrfs_file_write_iter+0x81/0x410 [btrfs]
  [72747.569836]  ? __kmalloc+0x16a/0x2c0
  [72747.569839]  do_iter_readv_writev+0x160/0x1c0
  [72747.569843]  do_iter_write+0x80/0x1b0
  [72747.569847]  vfs_writev+0x84/0x140
  [72747.569869]  ? btrfs_file_llseek+0x38/0x270 [btrfs]
  [72747.569873]  do_writev+0x65/0x100
  [72747.569876]  do_syscall_64+0x33/0x40
  [72747.569879]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

  [72747.569899] task:fsstress        state:D stack:    0 pid:841424 ppid:841417 flags:0x00004000
  [72747.569903] Call Trace:
  [72747.569906]  __schedule+0x296/0x760
  [72747.569909]  schedule+0x3c/0xa0
  [72747.569936]  try_flush_qgroup+0x95/0x140 [btrfs]
  [72747.569940]  ? finish_wait+0x80/0x80
  [72747.569967]  __btrfs_qgroup_reserve_meta+0x36/0x50 [btrfs]
  [72747.569989]  start_transaction+0x279/0x580 [btrfs]
  [72747.570014]  clone_copy_inline_extent+0x332/0x490 [btrfs]
  [72747.570041]  btrfs_clone+0x5b7/0x7a0 [btrfs]
  [72747.570068]  ? lock_extent_bits+0x64/0x90 [btrfs]
  [72747.570095]  btrfs_clone_files+0xfc/0x150 [btrfs]
  [72747.570122]  btrfs_remap_file_range+0x3d8/0x4a0 [btrfs]
  [72747.570126]  do_clone_file_range+0xed/0x200
  [72747.570131]  vfs_clone_file_range+0x37/0x110
  [72747.570134]  ioctl_file_clone+0x7d/0xb0
  [72747.570137]  do_vfs_ioctl+0x138/0x630
  [72747.570140]  __x64_sys_ioctl+0x62/0xc0
  [72747.570143]  do_syscall_64+0x33/0x40
  [72747.570146]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

So fix this by skipping the flush of delalloc for an inode that is
flagged with BTRFS_INODE_NO_DELALLOC_FLUSH, meaning it is currently under
such a special case of cloning an inline extent, when flushing delalloc
during qgroup metadata reservation.

The special cases for cloning inline extents were added in kernel 5.7 by
by commit 05a5a7621ce66c ("Btrfs: implement full reflink support for
inline extents"), while having qgroup metadata space reservation flushing
delalloc when low on space was added in kernel 5.9 by commit
c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get
-EDQUOT"). So use a "Fixes:" tag for the later commit to ease stable
kernel backports.

Reported-by: Wang Yugui <wangyugui@e16-tech.com>
Link: https://lore.kernel.org/linux-btrfs/20210421083137.31E3.409509F4@e16-tech.com/
Fixes: c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get -EDQUOT")
CC: stable@vger.kernel.org # 5.9+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>