Re: [syzbot] INFO: rcu detected stall in newstat

From: Dmitry Vyukov
Date: Mon Nov 29 2021 - 11:19:22 EST

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On Mon, 29 Nov 2021 at 14:13, Hillf Danton <hdanton@xxxxxxxx> wrote:
>
> On Mon, 29 Nov 2021 07:59:47 +0100 Dmitry Vyukov wrote:
> >On Sun, 28 Nov 2021 at 04:03, Hillf Danton wrote:
> >>
> >> On Tue, 03 Aug 2021 00:55:25 -0700
> >> > syzbot found the following issue on:
> >> >
> >> > HEAD commit: 7e96bf476270 Merge tag 'for-linus' of git://git.kernel.org..
> >> > git tree: upstream
> >> > console output: https://syzkaller.appspot.com/x/log.txt?x=111d1e2a300000
> >> > kernel config: https://syzkaller.appspot.com/x/.config?x=1dee114394f7d2c2
> >> > dashboard link: https://syzkaller.appspot.com/bug?extid=84ef57449019b1be878d
> >> > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
> >> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12f2aac9d00000
> >> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15470c66300000
> >> >
> >> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >> > Reported-by: syzbot+84ef57449019b1be878d@xxxxxxxxxxxxxxxxxxxxxxxxx
> >> >
> >> > mceusb 2-1:0.0: Error: urb status = -71
> >> > mceusb 5-1:0.0: Error: urb status = -71
> >> > mceusb 2-1:0.0: Error: urb status = -71
> >> > mceusb 5-1:0.0: Error: urb status = -71
> >> > mceusb 2-1:0.0: Error: urb status = -71
> >> > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> >> > (detected by 1, t=10502 jiffies, g=13449, q=1758)
> >> > rcu: All QSes seen, last rcu_preempt kthread activity 6502 (4295042261-4295035759), jiffies_till_next_fqs=1, root ->qsmask 0x0
> >> > rcu: rcu_preempt kthread starved for 6502 jiffies! g13449 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
> >> > rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
> >> > rcu: RCU grace-period kthread stack dump:
> >> > task:rcu_preempt state:R running task stack:29096 pid: 14 ppid: 2 flags:0x00004000
> >> > Call Trace:
> >> > context_switch kernel/sched/core.c:4683 [inline]
> >> > __schedule+0x93a/0x26f0 kernel/sched/core.c:5940
> >> > schedule+0xd3/0x270 kernel/sched/core.c:6019
> >> > schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1879
> >> > rcu_gp_fqs_loop kernel/rcu/tree.c:1996 [inline]
> >> > rcu_gp_kthread+0xd34/0x1980 kernel/rcu/tree.c:2169
> >> > kthread+0x3e5/0x4d0 kernel/kthread.c:319
> >> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> >> > rcu: Stack dump where RCU GP kthread last ran:
> >> > Sending NMI from CPU 1 to CPUs 0:
> >> > NMI backtrace for cpu 0
> >> > CPU: 0 PID: 8589 Comm: systemd-udevd Not tainted 5.14.0-rc3-syzkaller #0
> >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> > RIP: 0010:halt arch/x86/include/asm/irqflags.h:99 [inline]
> >> > RIP: 0010:kvm_wait+0xbb/0xf0 arch/x86/kernel/kvm.c:883
> >> > Code: 5b d9 47 00 8b 74 24 0c 48 8b 3c 24 eb 82 e8 6c de 47 00 eb 07 0f 00 2d c3 d3 55 08 fb f4 eb 9b eb 07 0f 00 2d b6 d3 55 08 f4 <eb> c5 89 74 24 0c 48 89 3c 24 e8 36 74 87 00 8b 74 24 0c 48 8b 3c
> >> > RSP: 0018:ffffc90001b87660 EFLAGS: 00000046
> >> > RAX: 0000000000000003 RBX: 0000000000000000 RCX: dffffc0000000000
> >> > RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff8b981e40
> >> > RBP: ffffffff8b981e40 R08: 0000000000000001 R09: ffffffff8b981e40
> >> > R10: fffffbfff17303c8 R11: 0000000000000001 R12: 0000000000000000
> >> > R13: fffffbfff17303c8 R14: 0000000000000001 R15: ffff8880b9c52980
> >> > FS: 00007f48df6fe8c0(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> >> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > CR2: 00007fff47502b08 CR3: 00000000141f0000 CR4: 00000000001506f0
> >> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> > Call Trace:
> >> > pv_wait arch/x86/include/asm/paravirt.h:597 [inline]
> >> > pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:470 [inline]
> >> > __pv_queued_spin_lock_slowpath+0x8b8/0xb40 kernel/locking/qspinlock.c:508
> >> > pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:585 [inline]
> >> > queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
> >> > queued_spin_lock include/asm-generic/qspinlock.h:85 [inline]
> >> > do_raw_spin_lock+0x200/0x2b0 kernel/locking/spinlock_debug.c:113
> >> > rcu_note_context_switch+0x294/0x16e0 kernel/rcu/tree_plugin.h:355
> >> > __schedule+0x21f/0x26f0 kernel/sched/core.c:5837
> >> > preempt_schedule_irq+0x4e/0x90 kernel/sched/core.c:6328
> >> > irqentry_exit+0x31/0x80 kernel/entry/common.c:427
> >> > asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> >> > RIP: 0010:__sanitizer_cov_trace_const_cmp1+0x77/0x80 kernel/kcov.c:272
> >> > Code: f0 72 27 41 0f b6 fb 41 0f b6 c9 48 83 c2 01 48 c7 44 30 e0 01 00 00 00 48 89 7c 30 e8 48 89 4c 30 f0 4c 89 54 d8 20 48 89 10 <5b> c3 0f 1f 80 00 00 00 00 53 41 89 fb 41 89 f1 bf 03 00 00 00 65
> >> > RSP: 0018:ffffc90001b87a18 EFLAGS: 00000246
> >> > RAX: 0000000000000000 RBX: 0000000000000075 RCX: ffff8880361be2c0
> >> > RDX: 0000000000000000 RSI: ffff8880361be2c0 RDI: 0000000000000003
> >> > RBP: 000000031dee9eb7 R08: 0000000000000000 R09: 0000000000000075
> >> > R10: ffffffff81c97ccd R11: 0000000000000000 R12: ffffc90001b87bec
> >> > R13: e2f55236f51925a6 R14: ffffc90001b87bb0 R15: ffff8880342d0825
> >> > link_path_walk.part.0+0x73d/0xd00 fs/namei.c:2272
> >> > link_path_walk fs/namei.c:2210 [inline]
> >> > path_lookupat+0xc8/0x860 fs/namei.c:2437
> >> > filename_lookup+0x1c6/0x5b0 fs/namei.c:2467
> >> > user_path_at include/linux/namei.h:57 [inline]
> >> > vfs_statx+0x142/0x390 fs/stat.c:203
> >> > vfs_fstatat fs/stat.c:225 [inline]
> >> > vfs_stat include/linux/fs.h:3382 [inline]
> >> > __do_sys_newstat+0x91/0x110 fs/stat.c:367
> >> > 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
> >> > RIP: 0033:0x7f48de570295
> >> > Code: 00 00 00 e8 5d 01 00 00 48 83 c4 18 c3 0f 1f 84 00 00 00 00 00 83 ff 01 48 89 f0 77 30 48 89 c7 48 89 d6 b8 04 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 03 f3 c3 90 48 8b 15 d1 db 2b 00 f7 d8 64 89
> >> > RSP: 002b:00007fff47503388 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
> >> > RAX: ffffffffffffffda RBX: 0000559e49eea790 RCX: 00007f48de570295
> >> > RDX: 00007fff47503390 RSI: 00007fff47503390 RDI: 00007fff47503440
> >> > RBP: 00007fff475034b0 R08: 000000000000c0c0 R09: 0000000000000000
> >> > R10: 00007fff475034c0 R11: 0000000000000246 R12: 00007fff475034c0
> >> > R13: 0000000000000001 R14: 0000559e49ed7a40 R15: 000000000000000e
> >> >
> >> > ================================
> >> > WARNING: inconsistent lock state
> >> > 5.14.0-rc3-syzkaller #0 Not tainted
> >> > --------------------------------
> >> > inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
> >> > ksoftirqd/1/19 [HC0[0]:SC1[1]:HE0:SE0] takes:
> >> > ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:543 [inline]
> >> > ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:709 [inline]
> >> > ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3922 [inline]
> >> > ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: rcu_sched_clock_irq+0xc9a/0x20c0 kernel/rcu/tree.c:2641
> >> > {IN-HARDIRQ-W} state was registered at:
> >> > lock_acquire kernel/locking/lockdep.c:5625 [inline]
> >> > lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5590
> >> > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> >> > _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:159
> >> > rcu_report_exp_cpu_mult+0x1c/0x280 kernel/rcu/tree_exp.h:237
> >> > flush_smp_call_function_queue+0x34b/0x640 kernel/smp.c:663
> >> > __sysvec_call_function_single+0x95/0x3d0 arch/x86/kernel/smp.c:248
> >> > sysvec_call_function_single+0x8e/0xc0 arch/x86/kernel/smp.c:243
> >> > asm_sysvec_call_function_single+0x12/0x20 arch/x86/include/asm/idtentry.h:646
> >> > lock_acquire+0x1ef/0x510 kernel/locking/lockdep.c:5593
> >> > down_write_killable+0x95/0x170 kernel/locking/rwsem.c:1417
> >> > mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
> >> > __bprm_mm_init fs/exec.c:257 [inline]
> >> > bprm_mm_init fs/exec.c:376 [inline]
> >> > alloc_bprm+0x3be/0x8f0 fs/exec.c:1521
> >> > kernel_execve+0x55/0x460 fs/exec.c:1941
> >> > call_usermodehelper_exec_async+0x2e3/0x580 kernel/umh.c:112
> >> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> >> > irq event stamp: 428515
> >> > hardirqs last enabled at (428514): [<ffffffff892ce380>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
> >> > hardirqs last enabled at (428514): [<ffffffff892ce380>] _raw_spin_unlock_irqrestore+0x50/0x70 kernel/locking/spinlock.c:191
> >> > hardirqs last disabled at (428515): [<ffffffff892a264b>] sysvec_apic_timer_interrupt+0xb/0xc0 arch/x86/kernel/apic/apic.c:1100
> >> > softirqs last enabled at (392664): [<ffffffff81456d5d>] run_ksoftirqd kernel/softirq.c:920 [inline]
> >> > softirqs last enabled at (392664): [<ffffffff81456d5d>] run_ksoftirqd+0x2d/0x60 kernel/softirq.c:912
> >> > softirqs last disabled at (392669): [<ffffffff81456d5d>] run_ksoftirqd kernel/softirq.c:920 [inline]
> >> > softirqs last disabled at (392669): [<ffffffff81456d5d>] run_ksoftirqd+0x2d/0x60 kernel/softirq.c:912
> >> >
> >> > other info that might help us debug this:
> >> > Possible unsafe locking scenario:
> >> >
> >> > CPU0
> >> > ----
> >> > lock(rcu_node_0);
> >> > <Interrupt>
> >> > lock(rcu_node_0);
> >> >
> >> > *** DEADLOCK ***
> >> >
> >> > 2 locks held by ksoftirqd/1/19:
> >> > #0: ffffc90000fafc58 ((&dum_hcd->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:35 [inline]
> >> > #0: ffffc90000fafc58 ((&dum_hcd->timer)){+.-.}-{0:0}, at: call_timer_fn+0xd5/0x6b0 kernel/time/timer.c:1409
> >> > #1: ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:543 [inline]
> >> > #1: ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:709 [inline]
> >> > #1: ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3922 [inline]
> >> > #1: ffffffff8b981e58 (rcu_node_0){?.-.}-{2:2}, at: rcu_sched_clock_irq+0xc9a/0x20c0 kernel/rcu/tree.c:2641
> >> >
> >> > stack backtrace:
> >> > CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.14.0-rc3-syzkaller #0
> >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> > Call Trace:
> >> > __dump_stack lib/dump_stack.c:88 [inline]
> >> > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
> >> > print_usage_bug kernel/locking/lockdep.c:203 [inline]
> >> > valid_state kernel/locking/lockdep.c:3933 [inline]
> >> > mark_lock_irq kernel/locking/lockdep.c:4136 [inline]
> >> > mark_lock.cold+0x61/0x8e kernel/locking/lockdep.c:4593
> >> > mark_held_locks+0x9f/0xe0 kernel/locking/lockdep.c:4194
> >> > __trace_hardirqs_on_caller kernel/locking/lockdep.c:4212 [inline]
> >> > lockdep_hardirqs_on_prepare kernel/locking/lockdep.c:4280 [inline]
> >> > lockdep_hardirqs_on_prepare+0x135/0x400 kernel/locking/lockdep.c:4232
> >> > trace_hardirqs_on+0x5b/0x1c0 kernel/trace/trace_preemptirq.c:49
> >> > asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:638
> >> > RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
> >> > RIP: 0010:_raw_spin_unlock_irqrestore+0x38/0x70 kernel/locking/spinlock.c:191
> >> > Code: 74 24 10 e8 5a 65 2d f8 48 89 ef e8 02 db 2d f8 81 e3 00 02 00 00 75 25 9c 58 f6 c4 02 75 2d 48 85 db 74 01 fb bf 01 00 00 00 <e8> 43 b5 21 f8 65 8b 05 4c 0c d5 76 85 c0 74 0a 5b 5d c3 e8 e0 10
> >> > RSP: 0018:ffffc90000faf9f0 EFLAGS: 00000206
> >> > RAX: 0000000000000006 RBX: 0000000000000200 RCX: 1ffffffff1fa5092
> >> > RDX: 0000000000000000 RSI: 0000000000000101 RDI: 0000000000000001
> >> > RBP: ffff888021db8000 R08: 0000000000000001 R09: ffffffff8fcd9977
> >> > R10: 0000000000000001 R11: 0000000000000000 R12: ffff888146dbe440
> >> > R13: ffff888016ba9600 R14: dffffc0000000000 R15: ffff8880242d7900
> >> > spin_unlock_irqrestore include/linux/spinlock.h:409 [inline]
> >> > dummy_timer+0x12f6/0x32b0 drivers/usb/gadget/udc/dummy_hcd.c:2001
> >> > call_timer_fn+0x1a5/0x6b0 kernel/time/timer.c:1419
> >> > expire_timers kernel/time/timer.c:1464 [inline]
> >> > __run_timers.part.0+0x675/0xa50 kernel/time/timer.c:1732
> >> > __run_timers kernel/time/timer.c:1713 [inline]
> >> > run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1745
> >> > __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
> >> > run_ksoftirqd kernel/softirq.c:920 [inline]
> >> > run_ksoftirqd+0x2d/0x60 kernel/softirq.c:912
> >> > smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164
> >> > kthread+0x3e5/0x4d0 kernel/kthread.c:319
> >> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> >> > ------------[ cut here ]------------
> >> > timer: dummy_timer+0x0/0x32b0 include/linux/list.h:112 preempt leak: 00000100 -> 00000101
> >> > WARNING: CPU: 1 PID: 19 at kernel/time/timer.c:1425 call_timer_fn+0x664/0x6b0 kernel/time/timer.c:1425
> >>
> >> Any light on how the dummy timer can trigger the warning is highly
> >> appreciated.
> >>
> >> Hillf
> >
> >Hi Hillf,
>
> Hi Dmitry
>
> >
> >syzbot says it's already fixed:
> >https://lore.kernel.org/lkml/0000000000006c5f7705d1c84b93@xxxxxxxxxx/
> >
> >The log was full of:
> >
> >mceusb 2-1:0.0: Error: urb status = -71
> >mceusb 5-1:0.0: Error: urb status = -71
> >mceusb 2-1:0.0: Error: urb status = -71
> >mceusb 5-1:0.0: Error: urb status = -71
> >mceusb 2-1:0.0: Error: urb status = -71
> >
> >The fix is in mceusb, so I think it all lines up well. I guess an urb
> >is resubmitted in an infinite loop or something similar.
> >
> >#syz fix:
> >media: mceusb: return without resubmitting URB in case of -EPROTO error.
>
> Thanks for sharing this and explaining.
>
> What is left is, with that fix put aside, is it likely for a timer
> callback hog that is running 100 seconds to trigger the preempt leak warning?
> Or is it due to something other than the hog?

Right, I missed the "preempt leak: 00000100 -> 00000101" warning. And
before that there is also "WARNING: inconsistent lock state" warning.
This reminds me of the issues we had with RCU/LOCKDEP before when an
RCU warning disabled LOCKDEP tracking, as the result LOCKDEP missed
part of events (e.g. tracked lock, but missed subsequent unlock) and
due to races/ordering issues it mis-reported them as nonsensical
reports.
+Peter, Boqun

> Hillf
>
> >
> >> > Modules linked in:
> >> > CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.14.0-rc3-syzkaller #0
> >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> > RIP: 0010:call_timer_fn+0x664/0x6b0 kernel/time/timer.c:1425
> >> > Code: e8 41 ae 10 00 89 da 4c 89 f6 48 c7 c7 a0 9d 8d 89 65 8b 0d 1e cd 9d 7e 81 e1 ff ff ff 7f c6 05 b0 ae f3 0b 01 e8 b7 b8 83 07 <0f> 0b e9 f4 fb ff ff e8 10 ae 10 00 0f 0b e9 6f fd ff ff e8 04 ae
> >> > RSP: 0018:ffffc90000fafc20 EFLAGS: 00010286
> >> > RAX: 0000000000000000 RBX: 0000000000000100 RCX: 0000000000000000
> >> > RDX: ffff888011e54140 RSI: ffffffff815cad15 RDI: fffff520001f5f76
> >> > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> >> > R10: ffffffff815c4b1e R11: 0000000000000000 R12: 0000000000000000
> >> > R13: 1ffff920001f5f85 R14: ffffffff859db710 R15: 0000000000000000
> >> > FS: 0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> >> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > CR2: 00007fb590071168 CR3: 000000001842b000 CR4: 00000000001506e0
> >> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> > Call Trace:
> >> > expire_timers kernel/time/timer.c:1464 [inline]
> >> > __run_timers.part.0+0x675/0xa50 kernel/time/timer.c:1732
> >> > __run_timers kernel/time/timer.c:1713 [inline]
> >> > run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1745
> >> > __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
> >> > run_ksoftirqd kernel/softirq.c:920 [inline]
> >> > run_ksoftirqd+0x2d/0x60 kernel/softirq.c:912
> >> > smpboot_thread_fn+0x645/0x9c0 kernel/smpboot.c:164
> >> > kthread+0x3e5/0x4d0 kernel/kthread.c:319
> >> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

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