BUG: soft lockup in _raw_spin_unlock

[syzbot]

Hello,

syzbot hit the following crash on bpf-next commit
878a4d328104fed86ea321c48a5245eed44fbe14 (Fri Apr 20 08:05:16 2018 +0000)
libbpf: fixed build error for samples/bpf/
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=9d16ae40a3249b00a524

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6223576852070400
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8733987683919582507
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+9d16ae...@syzkaller.appspotmail.com
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random: crng init done
watchdog: BUG: soft lockup - CPU#1 stuck for 134s! [syz-executor5:4541]
Modules linked in:
irq event stamp: 61201690
hardirqs last enabled at (61201689): [<ffffffff81c37e8f>]
seqcount_lockdep_reader_access include/linux/seqlock.h:83 [inline]
hardirqs last enabled at (61201689): [<ffffffff81c37e8f>]
read_seqcount_begin include/linux/seqlock.h:164 [inline]
hardirqs last enabled at (61201689): [<ffffffff81c37e8f>] read_seqbegin
include/linux/seqlock.h:433 [inline]
hardirqs last enabled at (61201689): [<ffffffff81c37e8f>]
read_seqbegin_or_lock include/linux/seqlock.h:529 [inline]
hardirqs last enabled at (61201689): [<ffffffff81c37e8f>]
d_walk+0x80f/0xc80 fs/dcache.c:1248
hardirqs last disabled at (61201690): [<ffffffff87800901>]
interrupt_entry+0xb1/0xf0 arch/x86/entry/entry_64.S:624
softirqs last enabled at (22717476): [<ffffffff87a00778>]
__do_softirq+0x778/0xaf5 kernel/softirq.c:311
softirqs last disabled at (22717407): [<ffffffff8146fce1>] invoke_softirq
kernel/softirq.c:365 [inline]
softirqs last disabled at (22717407): [<ffffffff8146fce1>]
irq_exit+0x1d1/0x200 kernel/softirq.c:405
CPU: 1 PID: 4541 Comm: syz-executor5 Not tainted 4.16.0+ #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783
[inline]
RIP: 0010:lock_release+0x4d4/0xa10 kernel/locking/lockdep.c:3942
RSP: 0018:ffff88019e567880 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: dffffc0000000000 RBX: 1ffff10033cacf15 RCX: 1ffff10033cab9dd
RDX: 1ffffffff11a30ed RSI: 0000000000000004 RDI: 0000000000000282
RBP: ffff88019e5679b0 R08: 1ffff10033cacf19 R09: ffffed003b5e46c2
R10: 0000000000000003 R11: 0000000000000003 R12: ffff88019e55c6c0
R13: ffff8801a8c5a7b8 R14: ffff88019e55c6c0 R15: ffff88019e5678c8
FS: 0000000000e6f940(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000e78978 CR3: 000000019ec29000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__raw_spin_unlock include/linux/spinlock_api_smp.h:150 [inline]
_raw_spin_unlock+0x1a/0x30 kernel/locking/spinlock.c:176
spin_unlock include/linux/spinlock.h:350 [inline]
d_walk+0x75f/0xc80 fs/dcache.c:1332
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: 0033:0x4550e7
RSP: 002b:00007fff59f01b28 EFLAGS: 00000206 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 0000000000000065 RCX: 00000000004550e7
RDX: 0000000000000000 RSI: 00007fff59f038d0 RDI: 00007fff59f038d0
RBP: 00007fff59f038d0 R08: 0000000000000000 R09: 0000000000000001
R10: 000000000000000a R11: 0000000000000206 R12: 0000000000e70940
R13: 0000000000000000 R14: 00000000000001ca R15: 0000000000019a6a
Code: 00 00 00 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 a3 03 00 00 48 83 3d
13 d0 75 07 00 0f 84 b8 02 00 00 48 8b bd e8 fe ff ff 57 9d <0f> 1f 44 00
00 48 b8 00 00 00 00 00 fc ff df 48 01 c3 48 c7 03


---
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[Dmitry Vyukov]

On Mon, Apr 23, 2018 at 10:34 AM, syzbot
<syzbot+9d16ae...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on bpf-next commit
> 878a4d328104fed86ea321c48a5245eed44fbe14 (Fri Apr 20 08:05:16 2018 +0000)
> libbpf: fixed build error for samples/bpf/
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=9d16ae40a3249b00a524
>
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=6223576852070400
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=-8733987683919582507
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+9d16ae...@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.

This looks like:

#syz dup: INFO: rcu detected stall in d_walk

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