INFO: task hung in synchronize_rcu (3)

INFO: task hung in synchronize_rcu (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4fa640dc Merge tag 'vfio-v5.8-rc7' of git://github.com/awi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12c738a0900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f87a5e4232fdb267
dashboard link: https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e2a437100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13af00e8900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0c6da80218456f1edc36@syzkaller.appspotmail.com

INFO: task kworker/0:5:2530 blocked for more than 144 seconds.
      Not tainted 5.8.0-rc6-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/0:5     D26496  2530      2 0x00004000
Workqueue: events free_ipc
Call Trace:
 context_switch kernel/sched/core.c:3458 [inline]
 __schedule+0x91f/0x2250 kernel/sched/core.c:4215
 schedule+0xd0/0x2a0 kernel/sched/core.c:4290
 schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1884
 do_wait_for_common kernel/sched/completion.c:85 [inline]
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
 __wait_rcu_gp+0x217/0x2d0 kernel/rcu/update.c:411
 synchronize_rcu+0x10a/0x180 kernel/rcu/tree.c:3430
 kern_unmount fs/namespace.c:3861 [inline]
 kern_unmount+0x67/0xe0 fs/namespace.c:3856
 free_ipc_ns ipc/namespace.c:123 [inline]
 free_ipc+0xbe/0x1b0 ipc/namespace.c:141
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
INFO: task syz-executor643:6834 blocked for more than 144 seconds.
      Not tainted 5.8.0-rc6-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor643 D24000  6834   6833 0xa0024002
Call Trace:
 context_switch kernel/sched/core.c:3458 [inline]
 __schedule+0x91f/0x2250 kernel/sched/core.c:4215
 schedule+0xd0/0x2a0 kernel/sched/core.c:4290
 schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1884
 do_wait_for_common kernel/sched/completion.c:85 [inline]
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
 rcu_barrier+0x2d1/0x4a0 kernel/rcu/tree.c:3661
 netdev_run_todo+0x100/0xac0 net/core/dev.c:9758
 tun_detach drivers/net/tun.c:711 [inline]
 tun_chr_close+0xf5/0x180 drivers/net/tun.c:3423
 __fput+0x33c/0x880 fs/file_table.c:281
 task_work_run+0xdd/0x190 kernel/task_work.c:135
 exit_task_work include/linux/task_work.h:25 [inline]
 do_exit+0xb72/0x2a40 kernel/exit.c:805
 do_group_exit+0x125/0x310 kernel/exit.c:903
 __do_sys_exit_group kernel/exit.c:914 [inline]
 __se_sys_exit_group kernel/exit.c:912 [inline]
 __ia32_sys_exit_group+0x3a/0x50 kernel/exit.c:912
 do_syscall_32_irqs_on+0x3f/0x60 arch/x86/entry/common.c:428
 __do_fast_syscall_32 arch/x86/entry/common.c:475 [inline]
 do_fast_syscall_32+0x7f/0x120 arch/x86/entry/common.c:503
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7fef569
Code: Bad RIP value.
RSP: 002b:00000000ffdacd8c EFLAGS: 00000292 ORIG_RAX: 00000000000000fc
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000080f7b38
RDX: 0000000000000000 RSI: 00000000080dffbc RDI: 00000000080f7b40
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1155:
 #0: ffffffff89bc11c0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:5779
2 locks held by kworker/0:5/2530:
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff8880aa026d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
 #1: ffffc9000804fda8 (free_ipc_work){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244
1 lock held by in:imklog/6529:
 #0: ffff88809f8eadf0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:826
1 lock held by syz-executor643/6834:
 #0: ffffffff89bc5728 (rcu_state.barrier_mutex){+.+.}-{3:3}, at: rcu_barrier+0x44/0x4a0 kernel/rcu/tree.c:3596

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1155 Comm: khungtaskd Not tainted 5.8.0-rc6-syzkaller #0
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+0x18f/0x20d lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
 watchdog+0xd7d/0x1000 kernel/hung_task.c:295
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.8.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:advance_sched+0x455/0x990 net/sched/sch_taprio.c:747
Code: 08 84 d2 0f 85 99 04 00 00 41 89 6c 24 20 e8 72 be 10 fb 48 b8 00 00 00 00 00 fc ff df 48 8b 54 24 08 48 c1 ea 03 80 3c 02 00 <0f> 85 4c 04 00 00 48 8b 7c 24 18 4c 89 63 e8 e8 d7 64 85 01 48 8d
RSP: 0018:ffffc90000007d78 EFLAGS: 00000046
RAX: dffffc0000000000 RBX: ffff88809dc04b40 RCX: ffffffff8662fdea
RDX: 1ffff11013b80965 RSI: ffffffff8662fe1e RDI: ffff8880a74c71a0
RBP: 0000000000000a00 R08: 0000000000000001 R09: ffff8880a74c71a3
R10: ffffed1014e98e34 R11: 0000000000000000 R12: ffff8880a74c7180
R13: 1623e9f81cc16400 R14: ffff8880a74c71a0 R15: 1623e9f81cc16400
FS:  0000000000000000(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000080a8270 CR3: 0000000009a79000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 __run_hrtimer kernel/time/hrtimer.c:1520 [inline]
 __hrtimer_run_queues+0x6a9/0xfc0 kernel/time/hrtimer.c:1584
 hrtimer_interrupt+0x32a/0x930 kernel/time/hrtimer.c:1646
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0x142/0x5e0 arch/x86/kernel/apic/apic.c:1097
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:711
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_apic_timer_interrupt+0xe0/0x120 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:585
RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
Code: ff 4c 89 ef e8 53 c8 ca f9 e9 8e fe ff ff 48 89 df e8 46 c8 ca f9 eb 8a cc cc cc cc e9 07 00 00 00 0f 00 2d 74 5f 60 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d 64 5f 60 00 f4 c3 cc cc 55 53 e8 29
RSP: 0018:ffffffff89a07c70 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffffffff89a86580 RSI: ffffffff87e85c48 RDI: ffffffff87e85c1e
RBP: ffff8880a7120064 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff8880a7120064
R13: 1ffffffff1340f98 R14: ffff8880a7120065 R15: 0000000000000001
 arch_safe_halt arch/x86/include/asm/paravirt.h:150 [inline]
 acpi_safe_halt+0x8d/0x110 drivers/acpi/processor_idle.c:111
 acpi_idle_do_entry+0x15c/0x1b0 drivers/acpi/processor_idle.c:525
 acpi_idle_enter+0x3f9/0xab0 drivers/acpi/processor_idle.c:651
 cpuidle_enter_state+0xff/0x960 drivers/cpuidle/cpuidle.c:235
 cpuidle_enter+0x4a/0xa0 drivers/cpuidle/cpuidle.c:346
 call_cpuidle kernel/sched/idle.c:126 [inline]
 cpuidle_idle_call kernel/sched/idle.c:214 [inline]
 do_idle+0x431/0x6d0 kernel/sched/idle.c:276
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:372
 start_kernel+0x9cb/0xa06 init/main.c:1043
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243


---
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syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: INFO: task hung in synchronize_rcu (3)

[syzbot]

syzbot has bisected this issue to:

commit 5a781ccbd19e4664babcbe4b4ead7aa2b9283d22
Author: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Date:   Sat Sep 29 00:59:43 2018 +0000

    tc: Add support for configuring the taprio scheduler

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=149057ef100000
start commit:   4fa640dc Merge tag 'vfio-v5.8-rc7' of git://github.com/awi..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=169057ef100000
console output: https://syzkaller.appspot.com/x/log.txt?x=129057ef100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f87a5e4232fdb267
dashboard link: https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e2a437100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13af00e8900000

Reported-by: syzbot+0c6da80218456f1edc36@syzkaller.appspotmail.com
Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] INFO: task hung in synchronize_rcu (3)

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 2d08935682ac5f6bfb70f7e6844ec27d4a245fa4
Author: Sean Christopherson <seanjc@google.com>
Date:   Fri Apr 15 00:43:41 2022 +0000

    KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16dc2e49f00000
start commit:   ea4424be1688 Merge tag 'mtd/fixes-for-5.17-rc8' of git://g..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=442f8ac61e60a75e
dashboard link: https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1685af9e700000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b09df1700000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] INFO: task hung in synchronize_rcu (3)

[Sean Christopherson]

On Tue, May 10, 2022, syzbot wrote:
> syzbot suspects this issue was fixed by commit:
> 
> commit 2d08935682ac5f6bfb70f7e6844ec27d4a245fa4
> Author: Sean Christopherson <seanjc@google.com>
> Date:   Fri Apr 15 00:43:41 2022 +0000
> 
>     KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16dc2e49f00000
> start commit:   ea4424be1688 Merge tag 'mtd/fixes-for-5.17-rc8' of git://g..
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=442f8ac61e60a75e
> dashboard link: https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1685af9e700000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b09df1700000
> 
> If the result looks correct, please mark the issue as fixed by replying with:
> 
> #syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

#syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()

Re: [syzbot] INFO: task hung in synchronize_rcu (3)

[Paolo Bonzini]

On 5/10/22 15:45, Sean Christopherson wrote:
>>
>>      KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
>>
>> bisection log:https://syzkaller.appspot.com/x/bisect.txt?x=16dc2e49f00000
>> start commit:   ea4424be1688 Merge tag 'mtd/fixes-for-5.17-rc8' of git://g..
>> git tree:       upstream
>> kernel config:https://syzkaller.appspot.com/x/.config?x=442f8ac61e60a75e
>> dashboard link:https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
>> syz repro:https://syzkaller.appspot.com/x/repro.syz?x=1685af9e700000
>> C reproducer:https://syzkaller.appspot.com/x/repro.c?x=11b09df1700000
>>
>> If the result looks correct, please mark the issue as fixed by replying with:
>>
>> #syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
>>
>> For information about bisection process see:https://goo.gl/tpsmEJ#bisection
> #syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> 

Are you sure? The hang is in synchronize_*rcu* and the testcase is 
unrelated to KVM.  It seems like the testcase is not 100% reproducible.

Paolo

Re: [syzbot] INFO: task hung in synchronize_rcu (3)

[Sean Christopherson]

On Tue, May 10, 2022, Paolo Bonzini wrote:
> On 5/10/22 15:45, Sean Christopherson wrote:
> > > 
> > >      KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> > > 
> > > bisection log:https://syzkaller.appspot.com/x/bisect.txt?x=16dc2e49f00000
> > > start commit:   ea4424be1688 Merge tag 'mtd/fixes-for-5.17-rc8' of git://g..
> > > git tree:       upstream
> > > kernel config:https://syzkaller.appspot.com/x/.config?x=442f8ac61e60a75e
> > > dashboard link:https://syzkaller.appspot.com/bug?extid=0c6da80218456f1edc36
> > > syz repro:https://syzkaller.appspot.com/x/repro.syz?x=1685af9e700000
> > > C reproducer:https://syzkaller.appspot.com/x/repro.c?x=11b09df1700000
> > > 
> > > If the result looks correct, please mark the issue as fixed by replying with:
> > > 
> > > #syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> > > 
> > > For information about bisection process see:https://goo.gl/tpsmEJ#bisection
> > #syz fix: KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()
> > 
> 
> Are you sure? The hang is in synchronize_*rcu* and the testcase is unrelated
> to KVM.  It seems like the testcase is not 100% reproducible.

Ugh, syzbot seems to have bundled multiple unrelated errors together.  The splat
that comes up first on the dashboard is definitely the KVM bug:

  INFO: task syz-executor500:19706 blocked for more than 143 seconds.
        Not tainted 5.17.0-rc7-syzkaller-00020-gea4424be1688 #0
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  task:syz-executor500 state:D stack:27048 pid:19706 ppid:  3644 flags:0x00000004
  Call Trace:
   <TASK>
   context_switch kernel/sched/core.c:4995 [inline]
   __schedule+0xa94/0x4910 kernel/sched/core.c:6304
   schedule+0xd2/0x260 kernel/sched/core.c:6377
   schedule_timeout+0x1db/0x2a0 kernel/time/timer.c:1857
   do_wait_for_common kernel/sched/completion.c:85 [inline]
   __wait_for_common+0x2af/0x360 kernel/sched/completion.c:106
   __synchronize_srcu+0x1f2/0x290 kernel/rcu/srcutree.c:930
   kvm_swap_active_memslots+0x410/0x800 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1473
   kvm_activate_memslot arch/x86/kvm/../../../virt/kvm/kvm_main.c:1595 [inline]
   kvm_create_memslot arch/x86/kvm/../../../virt/kvm/kvm_main.c:1660 [inline]
   kvm_set_memslot+0xa67/0x1010 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1772
   __kvm_set_memory_region+0xf02/0x11f0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1914
   kvm_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:1927 [inline]
   kvm_vm_ioctl_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:1939 [inline]
   kvm_vm_ioctl+0x51a/0x22c0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4492
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:874 [inline]
   __se_sys_ioctl fs/ioctl.c:860 [inline]
   __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

But there are multiple other errors that are indeed not the KVM bug.