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SubjectINFO: rcu detected stall in chrdev_open (2)
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Hello,

syzbot found the following crash on:

HEAD commit: 687dec9b Merge tag 'erofs-for-5.5-rc2-fixes' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bf5deae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=29784f46793e49c37812
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=165eba1ee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15c7ae61e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+29784f46793e49c37812@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 0, t=10502 jiffies, g=8389, q=39)
rcu: All QSes seen, last rcu_preempt kthread activity 10503
(4295039703-4295029200), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor062 R running task 26152 9337 9045 0x00004000
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:410 [inline]
check_cpu_stall kernel/rcu/tree_stall.h:538 [inline]
rcu_pending kernel/rcu/tree.c:2827 [inline]
rcu_sched_clock_irq.cold+0xaf4/0xc02 kernel/rcu/tree.c:2271
update_process_times+0x2d/0x70 kernel/time/timer.c:1726
tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1310
__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:kfree+0x239/0x2c0 mm/slab.c:3758
Code: 4f 7e 0f 85 20 fe ff ff e8 45 ee 4d ff e9 16 fe ff ff e8 8a 46 c8 ff
48 83 3d fa bb e0 07 00 0f 84 85 00 00 00 48 89 df 57 9d <0f> 1f 44 00 00
5b 41 5c 41 5d 41 5e 5d c3 e8 64 46 c8 ff 48 83 3d
RSP: 0018:ffffc900023e77f8 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000007 RBX: 0000000000000286 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000286
RBP: ffffc900023e7818 R08: ffff88809eebc300 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888095f8ebc0
R13: ffff8880aa4001c0 R14: ffffffff83daaa1a R15: dffffc0000000000
tty_free_file drivers/tty/tty_io.c:222 [inline]
tty_open+0x59a/0xbb0 drivers/tty/tty_io.c:2038
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4e6/0x1380 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3420 [inline]
path_openat+0x10df/0x4500 fs/namei.c:3537
do_filp_open+0x1a1/0x280 fs/namei.c:3567
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_openat fs/open.c:1124 [inline]
__se_sys_openat fs/open.c:1118 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1118
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4468f9
Code: e8 0c 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 5b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f505dd44db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00000000006dbc28 RCX: 00000000004468f9
RDX: 0000000000000000 RSI: 0000000020000380 RDI: ffffffffffffff9c
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007ffe574a581f R14: 00007f505dd459c0 R15: 000000000000002d
rcu: rcu_preempt kthread starved for 10546 jiffies! g8389 f0x2
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 29272 10 2 0x80004000
Call Trace:
context_switch kernel/sched/core.c:3385 [inline]
__schedule+0x934/0x1f90 kernel/sched/core.c:4081
schedule+0xdc/0x2b0 kernel/sched/core.c:4155
schedule_timeout+0x486/0xc50 kernel/time/timer.c:1895
rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
rcu_gp_kthread+0x9b2/0x18d0 kernel/rcu/tree.c:1821
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352


---
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