Re: INFO: rcu detected stall in shrink_dcache_parent

2018-04-14 Thread Tetsuo Handa 
Infinite loop inside shrink_dcache_parent() due to lack of cond_resched().
I can reproduce this issue by running the reproducer on one CPU (using "taskset 
-c 0").
Reverting commit 32785c0539b7e96f ("fs/dcache.c: add cond_resched() in 
shrink_dentry_list()")
solves this issue.

#syz dup: INFO: rcu detected stall in d_walk

Re: INFO: rcu detected stall in shrink_dcache_parent

2018-04-14 Thread Tetsuo Handa 
Infinite loop inside shrink_dcache_parent() due to lack of cond_resched().
I can reproduce this issue by running the reproducer on one CPU (using "taskset 
-c 0").
Reverting commit 32785c0539b7e96f ("fs/dcache.c: add cond_resched() in 
shrink_dentry_list()")
solves this issue.

#syz dup: INFO: rcu detected stall in d_walk

Re: INFO: rcu detected stall in shrink_dcache_parent

2018-04-13 Thread syzbot 

syzbot has found reproducer for the following crash on upstream commit
16e205cf42da1f497b10a4a24f563e6c0d574eec (Fri Apr 13 03:56:10 2018 +)
Merge tag 'drm-fixes-for-v4.17-rc1' of  
git://people.freedesktop.org/~airlied/linux
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=8e4a81166025b5b7fa66


So far this crash happened 13 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5369092034789376
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4909037686620160
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6422767771582464
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534

compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8e4a81166025b5b7f...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed.

INFO: rcu_sched self-detected stall on CPU
	1-...!: (124998 ticks this GP) idle=c6e/1/4611686018427387906  
softirq=11062/11062 fqs=0

 (t=125000 jiffies g=5220 c=5219 q=10)
rcu_sched kthread starved for 125000 jiffies! g5220 c5219 f0x0  
RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0

RCU grace-period kthread stack dump:
rcu_sched   R  running task23896 9  2 0x8000
Call Trace:
 context_switch kernel/sched/core.c:2848 [inline]
 __schedule+0x801/0x1e30 kernel/sched/core.c:3490
 schedule+0xef/0x430 kernel/sched/core.c:3549
 schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
 rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231
 kthread+0x345/0x410 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
NMI backtrace for cpu 1
CPU: 1 PID: 4547 Comm: syzkaller613030 Not tainted 4.16.0+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011

Call Trace:
 
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x151/0x192 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+0x175/0x1c2 kernel/rcu/tree.c:1376
 print_cpu_stall kernel/rcu/tree.c:1525 [inline]
 check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283
 __run_hrtimer kernel/time/hrtimer.c:1386 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448
 hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
 
RIP: 0010:__preempt_count_add arch/x86/include/asm/preempt.h:76 [inline]
RIP: 0010:__rcu_read_lock include/linux/rcupdate.h:83 [inline]
RIP: 0010:rcu_read_lock include/linux/rcupdate.h:630 [inline]
RIP: 0010:d_walk+0x476/0xc80 fs/dcache.c:1303
RSP: 0018:8801a93d79d8 EFLAGS: 0203 ORIG_RAX: ff13
RAX: 8801acbe6300 RBX: 8801a762b520 RCX: 815cbe3e
RDX:  RSI: 81c2a68f RDI: 8801a7644d20
RBP: 8801a93d7b58 R08: ed0034ec89a5 R09: ed0034ec89a4
R10: ed0034ec89a4 R11: 8801a7644d23 R12: 8801a7644ca0
R13: dc00 R14: 8801a7644d20 R15: 8801a93d7b30
 shrink_dcache_parent+0x179/0x230 fs/dcache.c:1486
 vfs_rmdir+0x202/0x470 fs/namei.c:3850
 do_rmdir+0x523/0x610 fs/namei.c:3911
 SYSC_rmdir fs/namei.c:3929 [inline]
 SyS_rmdir+0x1a/0x20 fs/namei.c:3927
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4464a7
RSP: 002b:7ffdd93b0718 EFLAGS: 0207 ORIG_RAX: 0054
RAX: ffda RBX: 0065 RCX: 004464a7
RDX:  RSI: 006d85f8 RDI: 7ffdd93b1f80
RBP: 7ffdd93b1f80 R08:  R09: 0001
R10: 0005 R11: 0207 R12: 025778a0
R13:  R14: 0008d71f R15: 7ffdd93b1978

Re: INFO: rcu detected stall in shrink_dcache_parent

2018-04-13 Thread syzbot 

syzbot has found reproducer for the following crash on upstream commit
16e205cf42da1f497b10a4a24f563e6c0d574eec (Fri Apr 13 03:56:10 2018 +)
Merge tag 'drm-fixes-for-v4.17-rc1' of  
git://people.freedesktop.org/~airlied/linux
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=8e4a81166025b5b7fa66


So far this crash happened 13 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5369092034789376
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4909037686620160
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6422767771582464
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534

compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8e4a81166025b5b7f...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed.

INFO: rcu_sched self-detected stall on CPU
	1-...!: (124998 ticks this GP) idle=c6e/1/4611686018427387906  
softirq=11062/11062 fqs=0

 (t=125000 jiffies g=5220 c=5219 q=10)
rcu_sched kthread starved for 125000 jiffies! g5220 c5219 f0x0  
RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0

RCU grace-period kthread stack dump:
rcu_sched   R  running task23896 9  2 0x8000
Call Trace:
 context_switch kernel/sched/core.c:2848 [inline]
 __schedule+0x801/0x1e30 kernel/sched/core.c:3490
 schedule+0xef/0x430 kernel/sched/core.c:3549
 schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
 rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231
 kthread+0x345/0x410 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
NMI backtrace for cpu 1
CPU: 1 PID: 4547 Comm: syzkaller613030 Not tainted 4.16.0+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011

Call Trace:
 
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x151/0x192 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+0x175/0x1c2 kernel/rcu/tree.c:1376
 print_cpu_stall kernel/rcu/tree.c:1525 [inline]
 check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283
 __run_hrtimer kernel/time/hrtimer.c:1386 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448
 hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
 
RIP: 0010:__preempt_count_add arch/x86/include/asm/preempt.h:76 [inline]
RIP: 0010:__rcu_read_lock include/linux/rcupdate.h:83 [inline]
RIP: 0010:rcu_read_lock include/linux/rcupdate.h:630 [inline]
RIP: 0010:d_walk+0x476/0xc80 fs/dcache.c:1303
RSP: 0018:8801a93d79d8 EFLAGS: 0203 ORIG_RAX: ff13
RAX: 8801acbe6300 RBX: 8801a762b520 RCX: 815cbe3e
RDX:  RSI: 81c2a68f RDI: 8801a7644d20
RBP: 8801a93d7b58 R08: ed0034ec89a5 R09: ed0034ec89a4
R10: ed0034ec89a4 R11: 8801a7644d23 R12: 8801a7644ca0
R13: dc00 R14: 8801a7644d20 R15: 8801a93d7b30
 shrink_dcache_parent+0x179/0x230 fs/dcache.c:1486
 vfs_rmdir+0x202/0x470 fs/namei.c:3850
 do_rmdir+0x523/0x610 fs/namei.c:3911
 SYSC_rmdir fs/namei.c:3929 [inline]
 SyS_rmdir+0x1a/0x20 fs/namei.c:3927
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4464a7
RSP: 002b:7ffdd93b0718 EFLAGS: 0207 ORIG_RAX: 0054
RAX: ffda RBX: 0065 RCX: 004464a7
RDX:  RSI: 006d85f8 RDI: 7ffdd93b1f80
RBP: 7ffdd93b1f80 R08:  R09: 0001
R10: 0005 R11: 0207 R12: 025778a0
R13:  R14: 0008d71f R15: 7ffdd93b1978

INFO: rcu detected stall in shrink_dcache_parent

2018-04-13 Thread syzbot 

Hello,

syzbot hit the following crash on upstream commit
c17b0aadb7d8f87de56a4a374a8131519c0f7422 (Thu Apr 12 16:15:48 2018 +)
Merge tag 'asm-generic' of  
git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=8e4a81166025b5b7fa66


So far this crash happened 5 times on upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5775899525906432
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534

compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8e4a81166025b5b7f...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.

If you forward the report, please keep this part and the footer.

TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending  
cookies.  Check SNMP counters.

INFO: rcu_sched detected stalls on CPUs/tasks:
(detected by 0, t=125007 jiffies, g=42063, c=42062, q=674)
All QSes seen, last rcu_sched kthread activity 125014  
(4295035404-4294910390), jiffies_till_next_fqs=3, root ->qsmask 0x0

syz-executor7   R  running task20696  4548   4539 0x0008
Call Trace:
 
 sched_show_task.cold.87+0x27a/0x301 kernel/sched/core.c:5325
 print_other_cpu_stall.cold.79+0x92f/0x9d2 kernel/rcu/tree.c:1481
 check_cpu_stall.isra.61+0x706/0xf50 kernel/rcu/tree.c:1599
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283
 __run_hrtimer kernel/time/hrtimer.c:1386 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448
 hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
 
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783  
[inline]

RIP: 0010:seqcount_lockdep_reader_access include/linux/seqlock.h:83 [inline]
RIP: 0010:read_seqcount_begin include/linux/seqlock.h:164 [inline]
RIP: 0010:read_seqbegin include/linux/seqlock.h:433 [inline]
RIP: 0010:read_seqbegin_or_lock include/linux/seqlock.h:529 [inline]
RIP: 0010:d_walk+0x840/0xc80 fs/dcache.c:1248
RSP: 0018:88018cc0f9d8 EFLAGS: 0293 ORIG_RAX: ff13
RAX: 88018cc02740 RBX: 0293 RCX: 1100319805fd
RDX:  RSI: 81c2a7ab RDI: 0293
RBP: 88018cc0fb58 R08: 88018cc02f78 R09: 0006
R10: 88018cc02740 R11:  R12: 0200
R13: dc00 R14: 110031981f7e R15: 88018cc0fb30
 shrink_dcache_parent+0x179/0x230 fs/dcache.c:1486
 vfs_rmdir+0x202/0x470 fs/namei.c:3850
 do_rmdir+0x523/0x610 fs/namei.c:3911
 SYSC_rmdir fs/namei.c:3929 [inline]
 SyS_rmdir+0x1a/0x20 fs/namei.c:3927
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454fe7
RSP: 002b:7ffc1ddb5118 EFLAGS: 0206 ORIG_RAX: 0054
RAX: ffda RBX: 0065 RCX: 00454fe7
RDX:  RSI: 7ffc1ddb6ec0 RDI: 7ffc1ddb6ec0
RBP: 7ffc1ddb6ec0 R08:  R09: 0001
R10: 000a R11: 0206 R12: 011ab940
R13:  R14: 04d0 R15: 0003b525
rcu_sched kthread starved for 125573 jiffies! g42063 c42062 f0x2  
RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1

RCU grace-period kthread stack dump:
rcu_sched   R  running task23592 9  2 0x8000
Call Trace:
 context_switch kernel/sched/core.c:2848 [inline]
 __schedule+0x801/0x1e30 kernel/sched/core.c:3490
 schedule+0xef/0x430 kernel/sched/core.c:3549
 schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
 rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231
 kthread+0x345/0x410 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzkal...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is  
merged

into any tree, please reply to this email with:
#syz fix: exact-commit-title
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug  
report.

Note: all commands must start from beginning

INFO: rcu detected stall in shrink_dcache_parent

2018-04-13 Thread syzbot 

Hello,

syzbot hit the following crash on upstream commit
c17b0aadb7d8f87de56a4a374a8131519c0f7422 (Thu Apr 12 16:15:48 2018 +)
Merge tag 'asm-generic' of  
git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=8e4a81166025b5b7fa66


So far this crash happened 5 times on upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5775899525906432
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534

compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8e4a81166025b5b7f...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.

If you forward the report, please keep this part and the footer.

TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending  
cookies.  Check SNMP counters.

INFO: rcu_sched detected stalls on CPUs/tasks:
(detected by 0, t=125007 jiffies, g=42063, c=42062, q=674)
All QSes seen, last rcu_sched kthread activity 125014  
(4295035404-4294910390), jiffies_till_next_fqs=3, root ->qsmask 0x0

syz-executor7   R  running task20696  4548   4539 0x0008
Call Trace:
 
 sched_show_task.cold.87+0x27a/0x301 kernel/sched/core.c:5325
 print_other_cpu_stall.cold.79+0x92f/0x9d2 kernel/rcu/tree.c:1481
 check_cpu_stall.isra.61+0x706/0xf50 kernel/rcu/tree.c:1599
 __rcu_pending kernel/rcu/tree.c:3356 [inline]
 rcu_pending kernel/rcu/tree.c:3401 [inline]
 rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283
 __run_hrtimer kernel/time/hrtimer.c:1386 [inline]
 __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448
 hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
 
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783  
[inline]

RIP: 0010:seqcount_lockdep_reader_access include/linux/seqlock.h:83 [inline]
RIP: 0010:read_seqcount_begin include/linux/seqlock.h:164 [inline]
RIP: 0010:read_seqbegin include/linux/seqlock.h:433 [inline]
RIP: 0010:read_seqbegin_or_lock include/linux/seqlock.h:529 [inline]
RIP: 0010:d_walk+0x840/0xc80 fs/dcache.c:1248
RSP: 0018:88018cc0f9d8 EFLAGS: 0293 ORIG_RAX: ff13
RAX: 88018cc02740 RBX: 0293 RCX: 1100319805fd
RDX:  RSI: 81c2a7ab RDI: 0293
RBP: 88018cc0fb58 R08: 88018cc02f78 R09: 0006
R10: 88018cc02740 R11:  R12: 0200
R13: dc00 R14: 110031981f7e R15: 88018cc0fb30
 shrink_dcache_parent+0x179/0x230 fs/dcache.c:1486
 vfs_rmdir+0x202/0x470 fs/namei.c:3850
 do_rmdir+0x523/0x610 fs/namei.c:3911
 SYSC_rmdir fs/namei.c:3929 [inline]
 SyS_rmdir+0x1a/0x20 fs/namei.c:3927
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454fe7
RSP: 002b:7ffc1ddb5118 EFLAGS: 0206 ORIG_RAX: 0054
RAX: ffda RBX: 0065 RCX: 00454fe7
RDX:  RSI: 7ffc1ddb6ec0 RDI: 7ffc1ddb6ec0
RBP: 7ffc1ddb6ec0 R08:  R09: 0001
R10: 000a R11: 0206 R12: 011ab940
R13:  R14: 04d0 R15: 0003b525
rcu_sched kthread starved for 125573 jiffies! g42063 c42062 f0x2  
RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1

RCU grace-period kthread stack dump:
rcu_sched   R  running task23592 9  2 0x8000
Call Trace:
 context_switch kernel/sched/core.c:2848 [inline]
 __schedule+0x801/0x1e30 kernel/sched/core.c:3490
 schedule+0xef/0x430 kernel/sched/core.c:3549
 schedule_timeout+0x138/0x240 kernel/time/timer.c:1801
 rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231
 kthread+0x345/0x410 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzkal...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is  
merged

into any tree, please reply to this email with:
#syz fix: exact-commit-title
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug  
report.

Note: all commands must start from beginning