From: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com
commit e804861bd4e69cc5fe1053eedcb024982dde8e48 upstream.
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+0xc75/0xe30 [btrfs] [372.977706] start_transaction+0x938/0x10a0 [btrfs] [372.997168] transaction_kthread+0x19d/0x3c0 [btrfs] [373.013021] ? btrfs_cleanup_transaction.isra.0+0xfc0/0xfc0 [btrfs] [373.031678] kthread+0x3b9/0x490 [373.047420] ? _raw_spin_unlock_irq+0x24/0x50 [373.064645] ? set_kthread_struct+0x100/0x100 [373.078571] ret_from_fork+0x22/0x30 [373.091197] </TASK> [373.105611] INFO: task btrfs:3145 blocked for more than 123 seconds. [373.114147] Not tainted 5.16.0-rc8 #7 [373.120401] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [373.130393] task:btrfs state:D stack: 0 pid: 3145 ppid: 3141 flags:0x00004000 [373.140998] Call Trace: [373.145501] <TASK> [373.149654] __schedule+0xb56/0x4850 [373.155306] ? io_schedule_timeout+0x190/0x190 [373.161965] ? lockdep_hardirqs_on+0x7e/0x100 [373.168469] ? _raw_spin_unlock_irqrestore+0x3e/0x60 [373.175468] schedule+0xe0/0x270 [373.180814] wait_for_commit+0x104/0x150 [btrfs] [373.187643] ? test_and_set_bit+0x20/0x20 [btrfs] [373.194772] ? kmem_cache_free+0x124/0x550 [373.201191] ? btrfs_put_transaction+0x69/0x3d0 [btrfs] [373.208738] ? finish_wait+0x270/0x270 [373.214704] ? __btrfs_end_transaction+0x347/0x7b0 [btrfs] [373.222342] btrfs_commit_transaction+0x44d/0x2610 [btrfs] [373.230233] ? join_transaction+0x255/0xe30 [btrfs] [373.237334] ? btrfs_record_root_in_trans+0x4d/0x170 [btrfs] [373.245251] ? btrfs_apply_pending_changes+0x50/0x50 [btrfs] [373.253296] relocate_block_group+0x105/0xc20 [btrfs] [373.260533] ? mutex_lock_io_nested+0x1270/0x1270 [373.267516] ? btrfs_wait_nocow_writers+0x85/0x180 [btrfs] [373.275155] ? merge_reloc_roots+0x710/0x710 [btrfs] [373.283602] ? btrfs_wait_ordered_extents+0xd30/0xd30 [btrfs] [373.291934] ? kmem_cache_free+0x124/0x550 [373.298180] btrfs_relocate_block_group+0x35c/0x930 [btrfs] [373.306047] btrfs_relocate_chunk+0x85/0x210 [btrfs] [373.313229] btrfs_balance+0x12f4/0x2d20 [btrfs] [373.320227] ? lock_release+0x3a9/0x6d0 [373.326206] ? btrfs_relocate_chunk+0x210/0x210 [btrfs] [373.333591] ? lock_is_held_type+0xe4/0x140 [373.340031] ? rcu_read_lock_sched_held+0x3f/0x70 [373.346910] btrfs_ioctl_balance+0x548/0x700 [btrfs] [373.354207] btrfs_ioctl+0x7f2/0x71b0 [btrfs] [373.360774] ? lockdep_hardirqs_on_prepare+0x410/0x410 [373.367957] ? lockdep_hardirqs_on_prepare+0x410/0x410 [373.375327] ? btrfs_ioctl_get_supported_features+0x20/0x20 [btrfs] [373.383841] ? find_held_lock+0x2c/0x110 [373.389993] ? lock_release+0x3a9/0x6d0 [373.395828] ? mntput_no_expire+0xf7/0xad0 [373.402083] ? lock_is_held_type+0xe4/0x140 [373.408249] ? vfs_fileattr_set+0x9f0/0x9f0 [373.414486] ? selinux_file_ioctl+0x349/0x4e0 [373.420938] ? trace_raw_output_lock+0xb4/0xe0 [373.427442] ? selinux_inode_getsecctx+0x80/0x80 [373.434224] ? lockdep_hardirqs_on+0x7e/0x100 [373.440660] ? force_qs_rnp+0x2a0/0x6b0 [373.446534] ? lock_is_held_type+0x9b/0x140 [373.452763] ? __blkcg_punt_bio_submit+0x1b0/0x1b0 [373.459732] ? security_file_ioctl+0x50/0x90 [373.466089] __x64_sys_ioctl+0x127/0x190 [373.472022] do_syscall_64+0x3b/0x90 [373.477513] entry_SYSCALL_64_after_hwframe+0x44/0xae [373.484823] RIP: 0033:0x7f8f4af7e2bb [373.490493] RSP: 002b:00007ffcbf936178 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [373.500197] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f8f4af7e2bb [373.509451] RDX: 00007ffcbf936220 RSI: 00000000c4009420 RDI: 0000000000000003 [373.518659] RBP: 00007ffcbf93774a R08: 0000000000000013 R09: 00007f8f4b02d4e0 [373.527872] R10: 00007f8f4ae87740 R11: 0000000000000246 R12: 0000000000000001 [373.537222] R13: 00007ffcbf936220 R14: 0000000000000000 R15: 0000000000000002 [373.546506] </TASK> [373.550878] INFO: task btrfs:3146 blocked for more than 123 seconds. [373.559383] Not tainted 5.16.0-rc8 #7 [373.565748] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [373.575748] task:btrfs state:D stack: 0 pid: 3146 ppid: 2168 flags:0x00000000 [373.586314] Call Trace: [373.590846] <TASK> [373.595121] __schedule+0xb56/0x4850 [373.600901] ? __lock_acquire+0x23db/0x5030 [373.607176] ? io_schedule_timeout+0x190/0x190 [373.613954] schedule+0xe0/0x270 [373.619157] schedule_timeout+0x168/0x220 [373.625170] ? usleep_range_state+0x150/0x150 [373.631653] ? mark_held_locks+0x9e/0xe0 [373.637767] ? do_raw_spin_lock+0x11e/0x250 [373.643993] ? lockdep_hardirqs_on_prepare+0x17b/0x410 [373.651267] ? _raw_spin_unlock_irq+0x24/0x50 [373.657677] ? lockdep_hardirqs_on+0x7e/0x100 [373.664103] wait_for_completion+0x163/0x250 [373.670437] ? bit_wait_timeout+0x160/0x160 [373.676585] btrfs_quota_disable+0x176/0x9a0 [btrfs] [373.683979] ? btrfs_quota_enable+0x12f0/0x12f0 [btrfs] [373.691340] ? down_write+0xd0/0x130 [373.696880] ? down_write_killable+0x150/0x150 [373.703352] btrfs_ioctl+0x3945/0x71b0 [btrfs] [373.710061] ? find_held_lock+0x2c/0x110 [373.716192] ? lock_release+0x3a9/0x6d0 [373.722047] ? __handle_mm_fault+0x23cd/0x3050 [373.728486] ? btrfs_ioctl_get_supported_features+0x20/0x20 [btrfs] [373.737032] ? set_pte+0x6a/0x90 [373.742271] ? do_raw_spin_unlock+0x55/0x1f0 [373.748506] ? lock_is_held_type+0xe4/0x140 [373.754792] ? vfs_fileattr_set+0x9f0/0x9f0 [373.761083] ? selinux_file_ioctl+0x349/0x4e0 [373.767521] ? selinux_inode_getsecctx+0x80/0x80 [373.774247] ? __up_read+0x182/0x6e0 [373.780026] ? count_memcg_events.constprop.0+0x46/0x60 [373.787281] ? up_write+0x460/0x460 [373.792932] ? security_file_ioctl+0x50/0x90 [373.799232] __x64_sys_ioctl+0x127/0x190 [373.805237] do_syscall_64+0x3b/0x90 [373.810947] entry_SYSCALL_64_after_hwframe+0x44/0xae [373.818102] RIP: 0033:0x7f1383ea02bb [373.823847] RSP: 002b:00007fffeb4d71f8 EFLAGS: 00000202 ORIG_RAX: 0000000000000010 [373.833641] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1383ea02bb [373.842961] RDX: 00007fffeb4d7210 RSI: 00000000c0109428 RDI: 0000000000000003 [373.852179] RBP: 0000000000000003 R08: 0000000000000003 R09: 0000000000000078 [373.861408] R10: 00007f1383daec78 R11: 0000000000000202 R12: 00007fffeb4d874a [373.870647] R13: 0000000000493099 R14: 0000000000000001 R15: 0000000000000000 [373.879838] </TASK> [373.884018] Showing all locks held in the system: [373.894250] 3 locks held by kworker/4:1/58: [373.900356] 1 lock held by khungtaskd/63: [373.906333] #0: ffffffff8945ff60 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 [373.917307] 3 locks held by kworker/u16:6/103: [373.923938] #0: ffff888127b4f138 ((wq_completion)btrfs-qgroup-rescan){+.+.}-{0:0}, at: process_one_work+0x712/0x1320 [373.936555] #1: ffff88810b817dd8 ((work_completion)(&work->normal_work)){+.+.}-{0:0}, at: process_one_work+0x73f/0x1320 [373.951109] #2: ffff888102dd4650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_qgroup_rescan_worker+0x1f6/0x10c0 [btrfs] [373.964027] 2 locks held by less/1803: [373.969982] #0: ffff88813ed56098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 [373.981295] #1: ffffc90000b3b2e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x9e2/0x1060 [373.992969] 1 lock held by btrfs-transacti/2347: [373.999893] #0: ffff88813d4887a8 (&fs_info->transaction_kthread_mutex){+.+.}-{3:3}, at: transaction_kthread+0xe3/0x3c0 [btrfs] [374.015872] 3 locks held by btrfs/3145: [374.022298] #0: ffff888102dd4460 (sb_writers#18){.+.+}-{0:0}, at: btrfs_ioctl_balance+0xc3/0x700 [btrfs] [374.034456] #1: ffff88813d48a0a0 (&fs_info->reclaim_bgs_lock){+.+.}-{3:3}, at: btrfs_balance+0xfe5/0x2d20 [btrfs] [374.047646] #2: ffff88813d488838 (&fs_info->cleaner_mutex){+.+.}-{3:3}, at: btrfs_relocate_block_group+0x354/0x930 [btrfs] [374.063295] 4 locks held by btrfs/3146: [374.069647] #0: ffff888102dd4460 (sb_writers#18){.+.+}-{0:0}, at: btrfs_ioctl+0x38b1/0x71b0 [btrfs] [374.081601] #1: ffff88813d488bb8 (&fs_info->subvol_sem){+.+.}-{3:3}, at: btrfs_ioctl+0x38fd/0x71b0 [btrfs] [374.094283] #2: ffff888102dd4650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_quota_disable+0xc8/0x9a0 [btrfs] [374.106885] #3: ffff88813d489800 (&fs_info->qgroup_ioctl_lock){+.+.}-{3:3}, at: btrfs_quota_disable+0xd5/0x9a0 [btrfs]
[374.126780] =============================================
To avoid the deadlock, wait for the qgroup rescan worker to complete before starting the transaction for the quota disable ioctl. Clear BTRFS_FS_QUOTA_ENABLE flag before the wait and the transaction to request the worker to complete. On transaction start failure, set the BTRFS_FS_QUOTA_ENABLE flag again. These BTRFS_FS_QUOTA_ENABLE flag changes can be done safely since the function btrfs_quota_disable is not called concurrently because of fs_info->subvol_sem.
Also check the BTRFS_FS_QUOTA_ENABLE flag in qgroup_rescan_init to avoid another qgroup rescan worker to start after the previous qgroup worker completed.
CC: stable@vger.kernel.org # 5.4+ Suggested-by: Nikolay Borisov nborisov@suse.com Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Shin'ichiro Kawasaki shinichiro.kawasaki@wdc.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/qgroup.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-)
--- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1185,9 +1185,24 @@ int btrfs_quota_disable(struct btrfs_fs_ struct btrfs_trans_handle *trans = NULL; int ret = 0;
+ /* + * We need to have subvol_sem write locked, to prevent races between + * concurrent tasks trying to disable quotas, because we will unlock + * and relock qgroup_ioctl_lock across BTRFS_FS_QUOTA_ENABLED changes. + */ + lockdep_assert_held_write(&fs_info->subvol_sem); + mutex_lock(&fs_info->qgroup_ioctl_lock); if (!fs_info->quota_root) goto out; + + /* + * Request qgroup rescan worker to complete and wait for it. This wait + * must be done before transaction start for quota disable since it may + * deadlock with transaction by the qgroup rescan worker. + */ + clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); + btrfs_qgroup_wait_for_completion(fs_info, false); mutex_unlock(&fs_info->qgroup_ioctl_lock);
/* @@ -1205,14 +1220,13 @@ int btrfs_quota_disable(struct btrfs_fs_ if (IS_ERR(trans)) { ret = PTR_ERR(trans); trans = NULL; + set_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); goto out; }
if (!fs_info->quota_root) goto out;
- clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); - btrfs_qgroup_wait_for_completion(fs_info, false); spin_lock(&fs_info->qgroup_lock); quota_root = fs_info->quota_root; fs_info->quota_root = NULL; @@ -3379,6 +3393,9 @@ qgroup_rescan_init(struct btrfs_fs_info btrfs_warn(fs_info, "qgroup rescan init failed, qgroup is not enabled"); ret = -EINVAL; + } else if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) { + /* Quota disable is in progress */ + ret = -EBUSY; }
if (ret) {