Message-ID: <CACT4Y+Y9=EXL9y9UwMTeOyc6ps+mrFd213opF5VqXBrkT48UYQ@mail.gmail.com>
Date:   Mon, 16 Apr 2018 11:11:36 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+5c73ae1814a4a5f3f31b@...kaller.appspotmail.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: INFO: rcu detected stall in select_collect

On Mon, Apr 16, 2018 at 10:59 AM, syzbot
<syzbot+5c73ae1814a4a5f3f31b@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on upstream commit
> 48023102b7078a6674516b1fe0d639669336049d (Fri Apr 13 23:55:41 2018 +0000)
> Merge branch 'overlayfs-linus' of
> git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=5c73ae1814a4a5f3f31b
>
> So far this crash happened 4 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=6222684371288064
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=-8852471259444315113
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Looks like:

#syz dup: INFO: rcu detected stall in d_walk


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5c73ae1814a4a5f3f31b@...kaller.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.
>
> INFO: rcu_sched detected stalls on CPUs/tasks:
>         (detected by 0, t=125007 jiffies, g=10417, c=10416, q=290)
> All QSes seen, last rcu_sched kthread activity 125014
> (4294860146-4294735132), jiffies_till_next_fqs=3, root ->qsmask 0x0
> syz-executor6   R  running task    21784  4569   4561 0x00000008
> Call Trace:
>  <IRQ>
>  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
>  </IRQ>
> RIP: 0010:__sanitizer_cov_trace_pc+0x14/0x50 kernel/kcov.c:94
> RSP: 0018:ffff88018d8bf8d8 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13
> RAX: ffff88018d8b4580 RBX: 1ffff10031b17f20 RCX: ffffffff81c1f494
> RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000005
> RBP: ffff88018d8bf8d8 R08: ffff88018d8b4580 R09: ffffed003b527e70
> R10: ffffed003b527e70 R11: ffff8801da93f383 R12: ffff88018d8bfbf0
> R13: ffff8801da93f300 R14: ffff88018d8bfbf8 R15: ffff88018d8bf9a0
>  select_collect+0x267/0x5f0 fs/dcache.c:1451
>  d_walk+0x3c3/0xc80 fs/dcache.c:1276
>  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: 0033:0x455087
> RSP: 002b:00007ffe0e80b288 EFLAGS: 00000206 ORIG_RAX: 0000000000000054
> RAX: ffffffffffffffda RBX: 0000000000000065 RCX: 0000000000455087
> RDX: 0000000000000000 RSI: 00007ffe0e80d030 RDI: 00007ffe0e80d030
> RBP: 00007ffe0e80d030 R08: 0000000000000000 R09: 0000000000000001
> R10: 0000000000000006 R11: 0000000000000206 R12: 0000000000fa5940
> R13: 0000000000000000 R14: 0000000000000117 R15: 0000000000010850
> rcu_sched kthread starved for 125603 jiffies! g10417 c10416 f0x2
> RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1
> RCU grace-period kthread stack dump:
> rcu_sched       R  running task    23896     9      2 0x80000000
> 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 syzkaller@...glegroups.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:
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> To mark this as a duplicate of another syzbot report, please reply with:
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> If it's a one-off invalid bug report, please reply with:
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