INFO: rcu detected stall in lo_ioctl

[syzbot]

Hello,

syzkaller hit the following crash on
6084b576dca2e898f5c101baef151f7bfdbb606d
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

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


INFO: rcu_sched self-detected stall on CPU
0-....: (124999 ticks this GP) idle=672/1/4611686018427387906
softirq=119929/119929 fqs=31199
(t=125000 jiffies g=55788 c=55787 q=388)
NMI backtrace for cpu 0
CPU: 0 PID: 17572 Comm: syz-executor5 Not tainted 4.15.0-rc3-next-20171214+
#67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xe9/0x14b lib/dump_stack.c:53
nmi_cpu_backtrace+0x149/0x150 lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x101/0x150 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
rcu_dump_cpu_stacks+0xa7/0xe8 kernel/rcu/tree.c:1375
print_cpu_stall kernel/rcu/tree.c:1524 [inline]
check_cpu_stall kernel/rcu/tree.c:1592 [inline]
__rcu_pending kernel/rcu/tree.c:3362 [inline]
rcu_pending kernel/rcu/tree.c:3424 [inline]
rcu_check_callbacks+0x7d9/0xa10 kernel/rcu/tree.c:2764
update_process_times+0x30/0x60 kernel/time/timer.c:1630
tick_sched_handle+0x32/0x80 kernel/time/tick-sched.c:162
tick_sched_timer+0x3e/0xa0 kernel/time/tick-sched.c:1148
__run_hrtimer kernel/time/hrtimer.c:1210 [inline]
__hrtimer_run_queues+0x10a/0x5e0 kernel/time/hrtimer.c:1274
hrtimer_interrupt+0xcd/0x260 kernel/time/hrtimer.c:1308
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
smp_apic_timer_interrupt+0x6d/0x2a0 arch/x86/kernel/apic/apic.c:1050
apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:920
</IRQ>
RIP: 0010:__sanitizer_cov_trace_pc+0x3f/0x50 kernel/kcov.c:106
RSP: 0018:ffffc90000ebfd90 EFLAGS: 00000216 ORIG_RAX: ffffffffffffff11
RAX: 0000000000010000 RBX: ffff8801df48ac00 RCX: ffffffff81d9d5c7
RDX: 0000000000010000 RSI: ffffc90004ee2000 RDI: 0000000000000286
RBP: ffffc90000ebfd90 R08: ffff88021fc1bd00 R09: ffffe8ffffc109a0
R10: ffffc90000ebfc40 R11: 0000000000000002 R12: ffff8801df48ad50
R13: ffff8801dd629880 R14: 0000000000000000 R15: ffff880215e2f7d8
is_loop_device drivers/block/loop.c:691 [inline]
loop_set_fd drivers/block/loop.c:879 [inline]
lo_ioctl+0x237/0xa40 drivers/block/loop.c:1358
__blkdev_driver_ioctl block/ioctl.c:303 [inline]
blkdev_ioctl+0x6c4/0xbb0 block/ioctl.c:601
block_ioctl+0x56/0x70 fs/block_dev.c:1860
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0xaf/0x840 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452a39
RSP: 002b:00007f2f757bac58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000758020 RCX: 0000000000452a39
RDX: 0000000000000014 RSI: 0000000000004c00 RDI: 0000000000000015
RBP: 000000000000013e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006efe70
R13: 00000000ffffffff R14: 00007f2f757bb6d4 R15: 0000000000000000
INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-... } 126268
jiffies s: 12409 root: 0x1/.
blocking rcu_node structures:
Task dump for CPU 0:
syz-executor5 R running task 0 17572 3376 0x0000000c
Call Trace:


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