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Subject[syzbot] possible deadlock in __queue_work
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Hello,

syzbot found the following issue on:

HEAD commit: 7af08140 Revert "gcov: clang: fix clang-11+ build"
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=107d2ee5d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=76c0382ceab56d34
dashboard link: https://syzkaller.appspot.com/bug?extid=6beae4000559d41d80f8

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+6beae4000559d41d80f8@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.12.0-rc8-syzkaller #0 Not tainted
------------------------------------------------------
migration/0/16 is trying to acquire lock:
ffff88802ca34a58 (&pool->lock){-.-.}-{2:2}, at: __queue_work+0x366/0xf00 kernel/workqueue.c:1454

but task is already holding lock:
ffffffff8bf8fec8 (tk_core.seq.seqcount){----}-{0:0}, at: multi_cpu_stop+0x15f/0x430 kernel/stop_machine.c:240

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (tk_core.seq.seqcount){----}-{0:0}:
seqcount_lockdep_reader_access include/linux/seqlock.h:103 [inline]
ktime_get+0x7c/0x470 kernel/time/timekeeping.c:827
ktime_get_ns include/linux/timekeeping.h:153 [inline]
delayacct_end kernel/delayacct.c:48 [inline]
__delayacct_blkio_end+0x8a/0x190 kernel/delayacct.c:82
delayacct_blkio_end include/linux/delayacct.h:125 [inline]
try_to_wake_up+0xc31/0x14a0 kernel/sched/core.c:3452
wake_page_function+0x22e/0x480 mm/filemap.c:1081
__wake_up_common+0x147/0x650 kernel/sched/wait.c:108
wake_up_page_bit+0x11e/0x320 mm/filemap.c:1114
unlock_page+0x177/0x240 mm/filemap.c:1431
end_buffer_async_read+0x5d3/0x7d0 fs/buffer.c:290
end_buffer_async_read_io+0xe0/0x300 fs/buffer.c:335
end_bio_bh_io_sync+0xe2/0x140 fs/buffer.c:3006
bio_endio+0x40f/0x810 block/bio.c:1451
req_bio_endio block/blk-core.c:265 [inline]
blk_update_request+0x68b/0x1480 block/blk-core.c:1456
scsi_end_request+0x7a/0x800 drivers/scsi/scsi_lib.c:570
scsi_io_completion+0x1df/0x1170 drivers/scsi/scsi_lib.c:970
scsi_softirq_done+0x12f/0x270 drivers/scsi/scsi_lib.c:1450
blk_complete_reqs+0x9d/0xd0 block/blk-mq.c:576
__do_softirq+0x29b/0x9f6 kernel/softirq.c:345
run_ksoftirqd kernel/softirq.c:652 [inline]
run_ksoftirqd+0x2d/0x60 kernel/softirq.c:644
smpboot_thread_fn+0x655/0x9e0 kernel/smpboot.c:165
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #1 (&p->pi_lock){-.-.}-{2:2}:
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:159
try_to_wake_up+0x98/0x14a0 kernel/sched/core.c:3345
create_worker+0x4e4/0x6d0 kernel/workqueue.c:1950
workqueue_init+0x5e4/0x8bf kernel/workqueue.c:6046
kernel_init_freeable+0x386/0x6c2 init/main.c:1521
kernel_init+0xd/0x1b8 init/main.c:1424
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #0 (&pool->lock){-.-.}-{2:2}:
check_prev_add kernel/locking/lockdep.c:2937 [inline]
check_prevs_add kernel/locking/lockdep.c:3060 [inline]
validate_chain kernel/locking/lockdep.c:3675 [inline]
__lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4901
lock_acquire kernel/locking/lockdep.c:5511 [inline]
lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
__queue_work+0x366/0xf00 kernel/workqueue.c:1454
queue_work_on+0xee/0x110 kernel/workqueue.c:1524
queue_work include/linux/workqueue.h:507 [inline]
pvclock_gtod_notify arch/x86/kvm/x86.c:7980 [inline]
pvclock_gtod_notify+0x4a4/0x590 arch/x86/kvm/x86.c:7967
notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
update_pvclock_gtod kernel/time/timekeeping.c:653 [inline]
timekeeping_update+0x2b3/0x4c0 kernel/time/timekeeping.c:749
change_clocksource+0x1ad/0x290 kernel/time/timekeeping.c:1454
multi_cpu_stop+0x15f/0x430 kernel/stop_machine.c:240
cpu_stopper_thread+0x20b/0x490 kernel/stop_machine.c:510
smpboot_thread_fn+0x655/0x9e0 kernel/smpboot.c:165
kthread+0x3b1/0x4a0 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:
&pool->lock --> &p->pi_lock --> tk_core.seq.seqcount

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(tk_core.seq.seqcount);
lock(&p->pi_lock);
lock(tk_core.seq.seqcount);
lock(&pool->lock);

*** DEADLOCK ***

3 locks held by migration/0/16:
#0: ffffffff8bf90058 (timekeeper_lock){-.-.}-{2:2}, at: change_clocksource+0x1a/0x290 kernel/time/timekeeping.c:1435
#1: ffffffff8bf8fec8 (tk_core.seq.seqcount){----}-{0:0}, at: multi_cpu_stop+0x15f/0x430 kernel/stop_machine.c:240
#2: ffffffff8bf718a0 (rcu_read_lock){....}-{1:2}, at: __queue_work+0xd0/0xf00 kernel/workqueue.c:1417

stack backtrace:
CPU: 0 PID: 16 Comm: migration/0 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Stopper: multi_cpu_stop+0x0/0x430 kernel/stop_machine.c:200 <- 0x0
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2128
check_prev_add kernel/locking/lockdep.c:2937 [inline]
check_prevs_add kernel/locking/lockdep.c:3060 [inline]
validate_chain kernel/locking/lockdep.c:3675 [inline]
__lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4901
lock_acquire kernel/locking/lockdep.c:5511 [inline]
lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
__queue_work+0x366/0xf00 kernel/workqueue.c:1454
queue_work_on+0xee/0x110 kernel/workqueue.c:1524
queue_work include/linux/workqueue.h:507 [inline]
pvclock_gtod_notify arch/x86/kvm/x86.c:7980 [inline]
pvclock_gtod_notify+0x4a4/0x590 arch/x86/kvm/x86.c:7967
notifier_call_chain+0xb5/0x200 kernel/notifier.c:83
update_pvclock_gtod kernel/time/timekeeping.c:653 [inline]
timekeeping_update+0x2b3/0x4c0 kernel/time/timekeeping.c:749
change_clocksource+0x1ad/0x290 kernel/time/timekeeping.c:1454
multi_cpu_stop+0x15f/0x430 kernel/stop_machine.c:240
cpu_stopper_thread+0x20b/0x490 kernel/stop_machine.c:510
smpboot_thread_fn+0x655/0x9e0 kernel/smpboot.c:165
kthread+0x3b1/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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