possible deadlock in start_transaction

From: syzbot
Date: Sun Oct 04 2020 - 00:30:25 EST

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Hello,

syzbot found the following issue on:

HEAD commit: ccc1d052 Merge tag 'dmaengine-fix-5.9' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f1fa5b900000
kernel config: https://syzkaller.appspot.com/x/.config?x=41b736b7ce1b3ea4
dashboard link: https://syzkaller.appspot.com/bug?extid=ec309a632856890f2635
compiler: gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ec309a632856890f2635@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc7-syzkaller #0 Not tainted
------------------------------------------------------
kworker/u4:6/8345 is trying to acquire lock:
ffff888091200640 (sb_internal#3){.+.+}-{0:0}, at: sb_start_intwrite include/linux/fs.h:1690 [inline]
ffff888091200640 (sb_internal#3){.+.+}-{0:0}, at: start_transaction+0xbe7/0x1170 fs/btrfs/transaction.c:624

but task is already holding lock:
ffffc900161ffda8 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #4 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}:
__flush_work+0x60e/0xac0 kernel/workqueue.c:3041
wb_shutdown+0x180/0x220 mm/backing-dev.c:355
bdi_unregister+0x174/0x590 mm/backing-dev.c:872
del_gendisk+0x820/0xa10 block/genhd.c:933
loop_remove drivers/block/loop.c:2192 [inline]
loop_control_ioctl drivers/block/loop.c:2291 [inline]
loop_control_ioctl+0x3b1/0x480 drivers/block/loop.c:2257
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #3 (loop_ctl_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
lo_open+0x19/0xd0 drivers/block/loop.c:1893
__blkdev_get+0x759/0x1aa0 fs/block_dev.c:1507
blkdev_get fs/block_dev.c:1639 [inline]
blkdev_open+0x227/0x300 fs/block_dev.c:1753
do_dentry_open+0x4b9/0x11b0 fs/open.c:817
do_open fs/namei.c:3251 [inline]
path_openat+0x1b9a/0x2730 fs/namei.c:3368
do_filp_open+0x17e/0x3c0 fs/namei.c:3395
do_sys_openat2+0x16d/0x420 fs/open.c:1168
do_sys_open fs/open.c:1184 [inline]
__do_sys_open fs/open.c:1192 [inline]
__se_sys_open fs/open.c:1188 [inline]
__x64_sys_open+0x119/0x1c0 fs/open.c:1188
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #2 (&bdev->bd_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
blkdev_put+0x30/0x520 fs/block_dev.c:1804
btrfs_close_bdev fs/btrfs/volumes.c:1117 [inline]
btrfs_close_bdev fs/btrfs/volumes.c:1107 [inline]
btrfs_close_one_device fs/btrfs/volumes.c:1133 [inline]
close_fs_devices.part.0+0x1a4/0x800 fs/btrfs/volumes.c:1161
close_fs_devices fs/btrfs/volumes.c:1193 [inline]
btrfs_close_devices+0x95/0x1f0 fs/btrfs/volumes.c:1179
close_ctree+0x688/0x6cb fs/btrfs/disk-io.c:4148
generic_shutdown_super+0x144/0x370 fs/super.c:464
kill_anon_super+0x36/0x60 fs/super.c:1108
btrfs_kill_super+0x38/0x50 fs/btrfs/super.c:2265
deactivate_locked_super+0x94/0x160 fs/super.c:335
deactivate_super+0xad/0xd0 fs/super.c:366
cleanup_mnt+0x3a3/0x530 fs/namespace.c:1118
task_work_run+0xdd/0x190 kernel/task_work.c:141
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop kernel/entry/common.c:165 [inline]
exit_to_user_mode_prepare+0x1e1/0x200 kernel/entry/common.c:192
syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:267
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
btrfs_finish_chunk_alloc+0x281/0xf90 fs/btrfs/volumes.c:5255
btrfs_create_pending_block_groups+0x2f3/0x700 fs/btrfs/block-group.c:2109
__btrfs_end_transaction+0xf5/0x690 fs/btrfs/transaction.c:916
btrfs_alloc_data_chunk_ondemand+0x2a1/0x670 fs/btrfs/delalloc-space.c:167
btrfs_fallocate+0x279/0x2900 fs/btrfs/file.c:3282
vfs_fallocate+0x48d/0x9d0 fs/open.c:309
ksys_fallocate fs/open.c:332 [inline]
__do_sys_fallocate fs/open.c:340 [inline]
__se_sys_fallocate fs/open.c:338 [inline]
__x64_sys_fallocate+0xcf/0x140 fs/open.c:338
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #0 (sb_internal#3){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4441
lock_acquire+0x1f3/0xaf0 kernel/locking/lockdep.c:5029
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write+0x228/0x450 fs/super.c:1672
sb_start_intwrite include/linux/fs.h:1690 [inline]
start_transaction+0xbe7/0x1170 fs/btrfs/transaction.c:624
find_free_extent_update_loop fs/btrfs/extent-tree.c:3789 [inline]
find_free_extent+0x25e1/0x2e60 fs/btrfs/extent-tree.c:4127
btrfs_reserve_extent+0x166/0x460 fs/btrfs/extent-tree.c:4206
cow_file_range+0x3de/0x9b0 fs/btrfs/inode.c:1063
btrfs_run_delalloc_range+0x2cf/0x1410 fs/btrfs/inode.c:1838
writepage_delalloc+0x150/0x460 fs/btrfs/extent_io.c:3439
__extent_writepage+0x441/0xd00 fs/btrfs/extent_io.c:3653
extent_write_cache_pages.constprop.0+0x69d/0x1040 fs/btrfs/extent_io.c:4249
extent_writepages+0xcd/0x2b0 fs/btrfs/extent_io.c:4370
do_writepages+0xec/0x290 mm/page-writeback.c:2352
__writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
wb_writeback+0x2ad/0xd40 fs/fs-writeback.c:1894
wb_do_writeback fs/fs-writeback.c:2039 [inline]
wb_workfn+0x2dc/0x13e0 fs/fs-writeback.c:2080
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

other info that might help us debug this:

Chain exists of:
sb_internal#3 --> loop_ctl_mutex --> (work_completion)(&(&wb->dwork)->work)

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock((work_completion)(&(&wb->dwork)->work));
lock(loop_ctl_mutex);
lock((work_completion)(&(&wb->dwork)->work));
lock(sb_internal#3);

*** DEADLOCK ***

2 locks held by kworker/u4:6/8345:
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff88821ade2938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
#1: ffffc900161ffda8 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244

stack backtrace:
CPU: 0 PID: 8345 Comm: kworker/u4:6 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-btrfs-6)
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x198/0x1fd lib/dump_stack.c:118
check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4441
lock_acquire+0x1f3/0xaf0 kernel/locking/lockdep.c:5029
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write+0x228/0x450 fs/super.c:1672
sb_start_intwrite include/linux/fs.h:1690 [inline]
start_transaction+0xbe7/0x1170 fs/btrfs/transaction.c:624
find_free_extent_update_loop fs/btrfs/extent-tree.c:3789 [inline]
find_free_extent+0x25e1/0x2e60 fs/btrfs/extent-tree.c:4127
btrfs_reserve_extent+0x166/0x460 fs/btrfs/extent-tree.c:4206
cow_file_range+0x3de/0x9b0 fs/btrfs/inode.c:1063
btrfs_run_delalloc_range+0x2cf/0x1410 fs/btrfs/inode.c:1838
writepage_delalloc+0x150/0x460 fs/btrfs/extent_io.c:3439
__extent_writepage+0x441/0xd00 fs/btrfs/extent_io.c:3653
extent_write_cache_pages.constprop.0+0x69d/0x1040 fs/btrfs/extent_io.c:4249
extent_writepages+0xcd/0x2b0 fs/btrfs/extent_io.c:4370
do_writepages+0xec/0x290 mm/page-writeback.c:2352
__writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
wb_writeback+0x2ad/0xd40 fs/fs-writeback.c:1894
wb_do_writeback fs/fs-writeback.c:2039 [inline]
wb_workfn+0x2dc/0x13e0 fs/fs-writeback.c:2080
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

---
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Next message: Raj, Ashok: "Re: [PATCH v7 0/5] Fix DPC hotplug race and enhance error handling"
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