Re: INFO: rcu detected stall in io_uring_release

[syzbot <syzbot+66243bb7126c410cefe6@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following crash on:

HEAD commit:    ac935d22 Add linux-next specific files for 20200415
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13a38f0a100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bc498783097e9019
dashboard link: https://syzkaller.appspot.com/bug?extid=66243bb7126c410cefe6
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=179b3b32100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+66243bb7126c410cefe6@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (10533 ticks this GP) idle=aea/1/0x4000000000000002 softirq=10553/10555 fqs=5249 
	(t=10501 jiffies g=12777 q=556)
NMI backtrace for cpu 0
CPU: 0 PID: 8729 Comm: syz-executor.3 Not tainted 5.7.0-rc1-next-20200415-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x231/0x27e lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:165 [inline]
 rcu_dump_cpu_stacks+0x19b/0x1e5 kernel/rcu/tree_stall.h:254
 print_cpu_stall kernel/rcu/tree_stall.h:475 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:549 [inline]
 rcu_pending kernel/rcu/tree.c:3225 [inline]
 rcu_sched_clock_irq.cold+0x55d/0xd00 kernel/rcu/tree.c:2296
 update_process_times+0x25/0x60 kernel/time/timer.c:1727
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176
 tick_sched_timer+0x4e/0x140 kernel/time/tick-sched.c:1320
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x5ca/0xed0 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x312/0x770 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1113 [inline]
 smp_apic_timer_interrupt+0x15b/0x600 arch/x86/kernel/apic/apic.c:1138
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:io_ring_ctx_wait_and_kill+0x98/0x5a0 fs/io_uring.c:7301
Code: 01 00 00 4d 89 f4 48 b8 00 00 00 00 00 fc ff df 4c 89 ed 49 c1 ec 03 48 c1 ed 03 49 01 c4 48 01 c5 eb 1c e8 ba 65 9d ff f3 90 <41> 80 3c 24 00 0f 85 53 04 00 00 48 83 bb 10 01 00 00 00 74 21 e8
RSP: 0018:ffffc900054d7a50 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
RAX: ffff888097c14400 RBX: ffff8880963a0000 RCX: 1ffff92000a9af37
RDX: 0000000000000000 RSI: ffffffff81d5ced6 RDI: ffff8880963a0300
RBP: ffffed1012c7402c R08: 0000000000000001 R09: ffffed1012c74061
R10: ffff8880963a0307 R11: ffffed1012c74060 R12: ffffed1012c74022
R13: ffff8880963a0160 R14: ffff8880963a0110 R15: ffffffff81d5d3e0
 io_uring_release+0x3e/0x50 fs/io_uring.c:7324
 __fput+0x33e/0x880 fs/file_table.c:280
 task_work_run+0xf4/0x1b0 kernel/task_work.c:123
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0xb53/0x2e10 kernel/exit.c:795
 do_group_exit+0x125/0x340 kernel/exit.c:893
 get_signal+0x47b/0x24e0 kernel/signal.c:2735
 do_signal+0x81/0x2240 arch/x86/kernel/signal.c:784
 exit_to_usermode_loop+0x26c/0x360 arch/x86/entry/common.c:161
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x6b1/0x7d0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45c829
Code: Bad RIP value.
RSP: 002b:00007fdd2a37fc78 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9
RAX: 0000000000000003 RBX: 00000000004e0ce0 RCX: 000000000045c829
RDX: 0000000000000000 RSI: 0000000020000580 RDI: 00000000000000f1
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000204 R14: 00000000004c425f R15: 00007fdd2a3806d4