INFO: rcu detected stall in ksys_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    94f2630b Merge tag '5.6-rc-small-smb3-fix-for-stable' of g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16aec776e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=99db4e42d047be3
dashboard link: https://syzkaller.appspot.com/bug?extid=4484fe09c3f9ab423f32
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17ab98d9e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1416f735e00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10249f66e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=12249f66e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14249f66e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4484fe09c3f9ab423f32@xxxxxxxxxxxxxxxxxxxxxxxxx

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
	(detected by 1, t=10502 jiffies, g=10641, q=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4295021069-4295010566), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor543 R  running task    27000 10496  10495 0x00000000
Call Trace:
 <IRQ>
 sched_show_task kernel/sched/core.c:5954 [inline]
 sched_show_task.cold+0x2ee/0x35d kernel/sched/core.c:5929
 print_other_cpu_stall kernel/rcu/tree_stall.h:430 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:558 [inline]
 rcu_pending kernel/rcu/tree.c:3030 [inline]
 rcu_sched_clock_irq.cold+0xb23/0xc37 kernel/rcu/tree.c:2276
 update_process_times+0x2d/0x70 kernel/time/timer.c:1726
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:171
 tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1314
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
RIP: 0010:lock_acquire+0x20b/0x410 kernel/locking/lockdep.c:4487
Code: 94 08 00 00 00 00 00 00 48 c1 e8 03 80 3c 10 00 0f 85 d3 01 00 00 48 83 3d 19 cf 58 08 00 0f 84 53 01 00 00 48 8b 7d c8 57 9d <0f> 1f 44 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 65 8b
RSP: 0018:ffffc90001f57ad0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff136753f RBX: ffff888089b4a140 RCX: ffffffff815a7ff0
RDX: dffffc0000000000 RSI: 0000000000000008 RDI: 0000000000000286
RBP: ffffc90001f57b18 R08: 1ffffffff16a137b R09: fffffbfff16a137c
R10: ffff888089b4aa00 R11: ffff888089b4a140 R12: ffffc90001fcae18
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000002
 rcu_lock_acquire include/linux/rcupdate.h:208 [inline]
 srcu_read_lock include/linux/srcu.h:155 [inline]
 vcpu_enter_guest+0x323d/0x6100 arch/x86/kvm/x86.c:8364
 vcpu_run arch/x86/kvm/x86.c:8445 [inline]
 kvm_arch_vcpu_ioctl_run+0x430/0x17b0 arch/x86/kvm/x86.c:8667
 kvm_vcpu_ioctl+0x4dc/0xfc0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2931
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4478a9
Code: e8 8c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb c4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdda97c7c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004478a9
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000009
RBP: 00000000006d2018 R08: 00000000004002e0 R09: 00000000004002e0
R10: 00000000004002e0 R11: 0000000000000246 R12: 0000000000404200
R13: 0000000000404290 R14: 0000000000000000 R15: 0000000000000000
rcu: rcu_preempt kthread starved for 10542 jiffies! g10641 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29224    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:3386 [inline]
 __schedule+0x934/0x1f90 kernel/sched/core.c:4082
 schedule+0xdc/0x2b0 kernel/sched/core.c:4156
 schedule_timeout+0x486/0xc50 kernel/time/timer.c:1895
 rcu_gp_fqs_loop kernel/rcu/tree.c:1658 [inline]
 rcu_gp_kthread+0xa10/0x1940 kernel/rcu/tree.c:1818
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352


---
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