Re: WARNING in io_disable_sqo_submit

[syzbot <syzbot+2f5d1785dc624932da78@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in io_sq_thread_stop

INFO: task kworker/u4:0:8 blocked for more than 143 seconds.
      Not tainted 5.11.0-rc1-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:0    state:D stack:24056 pid:    8 ppid:     2 flags:0x00004000
Workqueue: events_unbound io_ring_exit_work
Call Trace:
 context_switch kernel/sched/core.c:4313 [inline]
 __schedule+0x90c/0x21a0 kernel/sched/core.c:5064
 schedule+0xcf/0x270 kernel/sched/core.c:5143
 schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1854
 do_wait_for_common kernel/sched/completion.c:85 [inline]
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
 kthread_park+0x122/0x1b0 kernel/kthread.c:557
 io_sq_thread_park fs/io_uring.c:7445 [inline]
 io_sq_thread_park fs/io_uring.c:7439 [inline]
 io_sq_thread_stop+0xfe/0x570 fs/io_uring.c:7463
 io_finish_async fs/io_uring.c:7481 [inline]
 io_ring_ctx_free fs/io_uring.c:8646 [inline]
 io_ring_exit_work+0x62/0x6d0 fs/io_uring.c:8739
 process_one_work+0x98d/0x15f0 kernel/workqueue.c:2275
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Showing all locks held in the system:
3 locks held by kworker/u4:0/8:
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff888010069138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x871/0x15f0 kernel/workqueue.c:2246
 #1: ffffc90000cd7da8 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x15f0 kernel/workqueue.c:2250
 #2: ffff88801bfd4870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7444 [inline]
 #2: ffff88801bfd4870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7439 [inline]
 #2: ffff88801bfd4870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_stop+0xd6/0x570 fs/io_uring.c:7463
1 lock held by khungtaskd/1647:
 #0: ffffffff8b373aa0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6254
1 lock held by in:imklog/8164:
 #0: ffff8880151b8870 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:947
2 locks held by kworker/u4:6/8415:
2 locks held by kworker/0:4/8690:
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff88801007c538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x871/0x15f0 kernel/workqueue.c:2246
 #1: ffffc9000288fda8 ((work_completion)(&rew.rew_work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x15f0 kernel/workqueue.c:2250
1 lock held by syz-executor.3/8865:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206
1 lock held by syz-executor.2/8867:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206
2 locks held by syz-executor.5/8869:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206
 #1: ffffffff8b37c368 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:290 [inline]
 #1: ffffffff8b37c368 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x4f2/0x610 kernel/rcu/tree_exp.h:836
1 lock held by syz-executor.4/8870:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206
1 lock held by syz-executor.0/8872:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206
1 lock held by syz-executor.1/8873:
 #0: ffff888146ddcd88 (&xt[i].mutex){+.+.}-{3:3}, at: xt_find_table_lock+0x41/0x540 net/netfilter/x_tables.c:1206

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1647 Comm: khungtaskd Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
 nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
 watchdog+0xd43/0xfa0 kernel/hung_task.c:294
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 8415 Comm: kworker/u4:6 Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_nc_worker
RIP: 0010:__this_cpu_preempt_check+0xd/0x20 lib/smp_processor_id.c:70
Code: 00 00 48 c7 c6 00 d9 9e 89 48 c7 c7 40 d9 9e 89 e9 98 fe ff ff 0f 1f 84 00 00 00 00 00 55 48 89 fd 0f 1f 44 00 00 48 89 ee 5d <48> c7 c7 80 d9 9e 89 e9 77 fe ff ff cc cc cc cc cc cc cc 0f 1f 44
RSP: 0018:ffffc9000c507af0 EFLAGS: 00000046
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 1ffffffff1a077ab
RDX: 0000000000000000 RSI: ffffffff894bac40 RDI: ffffffff894bac40
RBP: ffffffff8b3739e0 R08: 0000000000000000 R09: ffffffff8d038b8f
R10: fffffbfff1a07171 R11: 0000000000000000 R12: 0000000000000001
R13: ffff88802f858bc0 R14: 00000000ffffffff R15: ffffffff889a5430
FS:  0000000000000000(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbcc03ca000 CR3: 0000000011523000 CR4: 0000000000350ef0
Call Trace:
 lockdep_recursion_inc kernel/locking/lockdep.c:432 [inline]
 lock_is_held_type+0x34/0x100 kernel/locking/lockdep.c:5475
 lock_is_held include/linux/lockdep.h:271 [inline]
 rcu_read_lock_sched_held+0x3a/0x70 kernel/rcu/update.c:123
 trace_lock_release include/trace/events/lock.h:58 [inline]
 lock_release+0x5b7/0x710 kernel/locking/lockdep.c:5448
 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:174 [inline]
 _raw_spin_unlock_bh+0x12/0x30 kernel/locking/spinlock.c:207
 spin_unlock_bh include/linux/spinlock.h:399 [inline]
 batadv_nc_purge_paths+0x2a5/0x3a0 net/batman-adv/network-coding.c:467
 batadv_nc_worker+0x831/0xe50 net/batman-adv/network-coding.c:716
 process_one_work+0x98d/0x15f0 kernel/workqueue.c:2275
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296


Tested on:

commit:         a1235e44 io_uring: cancel all requests on task exit
git tree:       git://git.kernel.dk/linux-block io_uring-5.11
console output: https://syzkaller.appspot.com/x/log.txt?x=10c53584d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c6b6b5cccb0f38f2
dashboard link: https://syzkaller.appspot.com/bug?extid=2f5d1785dc624932da78
compiler:       gcc (GCC) 10.1.0-syz 20200507