btrfs: fix deadlock between quota disable and qgroup rescan worker

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix deadlock between quota disable and qgroup rescan worker

Quota disable ioctl starts a transaction before waiting for the qgroup

rescan worker completes. However, this wait can be infinite and results

in deadlock because of circular dependency among the quota disable

ioctl, the qgroup rescan worker and the other task with transaction such

as block group relocation task.

The deadlock happens with the steps following:

1) Task A calls ioctl to disable quota. It starts a transaction and

waits for qgroup rescan worker completes.

2) Task B such as block group relocation task starts a transaction and

joins to the transaction that task A started. Then task B commits to

the transaction. In this commit, task B waits for a commit by task A.

3) Task C as the qgroup rescan worker starts its job and starts a

transaction. In this transaction start, task C waits for completion

of the transaction that task A started and task B committed.

This deadlock was found with fstests test case btrfs/115 and a zoned

null_blk device. The test case enables and disables quota, and the

block group reclaim was triggered during the quota disable by chance.

The deadlock was also observed by running quota enable and disable in

parallel with 'btrfs balance' command on regular null_blk devices.

An example report of the deadlock:

[372.469894] INFO: task kworker/u16:6:103 blocked for more than 122 seconds.

[372.479944] Not tainted 5.16.0-rc8 #7

[372.485067] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

[372.493898] task:kworker/u16:6 state:D stack: 0 pid: 103 ppid: 2 flags:0x00004000

[372.503285] Workqueue: btrfs-qgroup-rescan btrfs_work_helper [btrfs]

[372.510782] Call Trace:

[372.514092] <TASK>

[372.521684] __schedule+0xb56/0x4850

[372.530104] ? io_schedule_timeout+0x190/0x190

[372.538842] ? lockdep_hardirqs_on+0x7e/0x100

[372.547092] ? _raw_spin_unlock_irqrestore+0x3e/0x60

[372.555591] schedule+0xe0/0x270

[372.561894] btrfs_commit_transaction+0x18bb/0x2610 [btrfs]

[372.570506] ? btrfs_apply_pending_changes+0x50/0x50 [btrfs]

[372.578875] ? free_unref_page+0x3f2/0x650

[372.585484] ? finish_wait+0x270/0x270

[372.591594] ? release_extent_buffer+0x224/0x420 [btrfs]

[372.599264] btrfs_qgroup_rescan_worker+0xc13/0x10c0 [btrfs]

[372.607157] ? lock_release+0x3a9/0x6d0

[372.613054] ? btrfs_qgroup_account_extent+0xda0/0xda0 [btrfs]

[372.620960] ? do_raw_spin_lock+0x11e/0x250

[372.627137] ? rwlock_bug.part.0+0x90/0x90

[372.633215] ? lock_is_held_type+0xe4/0x140

[372.639404] btrfs_work_helper+0x1ae/0xa90 [btrfs]

[372.646268] process_one_work+0x7e9/0x1320

[372.652321] ? lock_release+0x6d0/0x6d0

[372.658081] ? pwq_dec_nr_in_flight+0x230/0x230

[372.664513] ? rwlock_bug.part.0+0x90/0x90

[372.670529] worker_thread+0x59e/0xf90

[372.676172] ? process_one_work+0x1320/0x1320

[372.682440] kthread+0x3b9/0x490

[372.687550] ? _raw_spin_unlock_irq+0x24/0x50

[372.693811] ? set_kthread_struct+0x100/0x100

[372.700052] ret_from_fork+0x22/0x30

[372.705517] </TASK>

[372.709747] INFO: task btrfs-transacti:2347 blocked for more than 123 seconds.

[372.729827] Not tainted 5.16.0-rc8 #7

[372.745907] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

[372.767106] task:btrfs-transacti state:D stack: 0 pid: 2347 ppid: 2 flags:0x00004000

[372.787776] Call Trace:

[372.801652] <TASK>

[372.812961] __schedule+0xb56/0x4850

[372.830011] ? io_schedule_timeout+0x190/0x190

[372.852547] ? lockdep_hardirqs_on+0x7e/0x100

[372.871761] ? _raw_spin_unlock_irqrestore+0x3e/0x60

[372.886792] schedule+0xe0/0x270

[372.901685] wait_current_trans+0x22c/0x310 [btrfs]

[372.919743] ? btrfs_put_transaction+0x3d0/0x3d0 [btrfs]

[372.938923] ? finish_wait+0x270/0x270

[372.959085] ? join_transaction+0xc7

---truncated---