INFO: rcu detected stall in v4l2_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4520f06b Linux 4.14.175
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12dc57fbe00000
kernel config: https://syzkaller.appspot.com/x/.config?x=93cf891381c0c347
dashboard link: https://syzkaller.appspot.com/bug?extid=693f672db1478cfd70d9
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+693f67...@syzkaller.appspotmail.com

INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 0, t=10502 jiffies, g=3440, c=3439, q=143)
All QSes seen, last rcu_preempt kthread activity 10502 (4294970676-4294960174), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.4 R running task 26768 10049 6356 0x8000000a
Call Trace:
<IRQ>
sched_show_task kernel/sched/core.c:5168 [inline]
sched_show_task.cold+0x2e3/0x347 kernel/sched/core.c:5143
print_other_cpu_stall kernel/rcu/tree.c:1501 [inline]
check_cpu_stall kernel/rcu/tree.c:1616 [inline]
__rcu_pending kernel/rcu/tree.c:3390 [inline]
rcu_pending kernel/rcu/tree.c:3452 [inline]
rcu_check_callbacks.cold+0xd3f/0xdaa kernel/rcu/tree.c:2792
update_process_times+0x29/0x60 kernel/time/timer.c:1590
tick_sched_handle+0x7d/0x150 kernel/time/tick-sched.c:165
tick_sched_timer+0x3e/0x120 kernel/time/tick-sched.c:1223
__run_hrtimer kernel/time/hrtimer.c:1223 [inline]
__hrtimer_run_queues+0x25c/0xbb0 kernel/time/hrtimer.c:1287
hrtimer_interrupt+0x1e6/0x5e0 kernel/time/hrtimer.c:1321
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1075 [inline]
smp_apic_timer_interrupt+0x117/0x5e0 arch/x86/kernel/apic/apic.c:1100
apic_timer_interrupt+0x8f/0xa0 arch/x86/entry/entry_64.S:792
</IRQ>
RIP: 0010:pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:411 [inline]
RIP: 0010:__pv_queued_spin_lock_slowpath+0x264/0x950 kernel/locking/qspinlock.c:465
RSP: 0018:ffff88804d48f3b8 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff10
RAX: 0000000000000003 RBX: ffff8880aea2c0c0 RCX: fffffbfff0fc106c
RDX: 0000000000006360 RSI: 0000000000000001 RDI: 0000000000000282
RBP: ffffffff87e08360 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffffffff87e08361 R15: ffffed1015d45820
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:669 [inline]
queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:52 [inline]
queued_spin_lock include/asm-generic/qspinlock.h:90 [inline]
do_raw_spin_lock+0x189/0x230 kernel/locking/spinlock_debug.c:113
spin_lock include/linux/spinlock.h:317 [inline]
find_vmap_area+0x1a/0x110 mm/vmalloc.c:770
find_vm_area mm/vmalloc.c:1475 [inline]
vmalloc_user+0x61/0x100 mm/vmalloc.c:1890
vb2_vmalloc_alloc+0xc9/0x270 drivers/media/v4l2-core/videobuf2-vmalloc.c:48
__vb2_buf_mem_alloc drivers/media/v4l2-core/videobuf2-core.c:208 [inline]
__vb2_queue_alloc+0x47a/0xd90 drivers/media/v4l2-core/videobuf2-core.c:361
vb2_core_reqbufs+0x376/0xa80 drivers/media/v4l2-core/videobuf2-core.c:719
__vb2_init_fileio+0x2f1/0xa80 drivers/media/v4l2-core/videobuf2-core.c:2239
__vb2_perform_fileio+0x9be/0xe40 drivers/media/v4l2-core/videobuf2-core.c:2358
vb2_fop_write+0x1ef/0x3d0 drivers/media/v4l2-core/videobuf2-v4l2.c:871
v4l2_write+0x19a/0x200 drivers/media/v4l2-core/v4l2-dev.c:326
__vfs_write+0xe4/0x630 fs/read_write.c:480
__kernel_write+0xf5/0x330 fs/read_write.c:501
write_pipe_buf+0x143/0x1b0 fs/splice.c:797
splice_from_pipe_feed fs/splice.c:502 [inline]
__splice_from_pipe+0x332/0x740 fs/splice.c:626
splice_from_pipe+0xc6/0x120 fs/splice.c:661
default_file_splice_write+0x37/0x80 fs/splice.c:809
do_splice_from fs/splice.c:851 [inline]
direct_splice_actor+0x115/0x160 fs/splice.c:1018
splice_direct_to_actor+0x27e/0x730 fs/splice.c:973
do_splice_direct+0x164/0x210 fs/splice.c:1061
do_sendfile+0x469/0xaf0 fs/read_write.c:1441
SYSC_sendfile64 fs/read_write.c:1496 [inline]
SyS_sendfile64+0x9b/0x110 fs/read_write.c:1488
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45c889
RSP: 002b:00007f9e967e8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f9e967e96d4 RCX: 000000000045c889
RDX: 00000000200000c0 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000eefffdef R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000008d4 R14: 00000000004cb7c6 R15: 000000000076bf0c
rcu_preempt kthread starved for 10502 jiffies! g3440 c3439 f0x2 RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1
rcu_preempt R running task 29920 8 2 0x80000000
Call Trace:
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_timeout+0x43c/0xe40 kernel/time/timer.c:1746
rcu_gp_kthread+0xb8e/0x1ce0 kernel/rcu/tree.c:2255
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.