INFO: task hung in utimes_common

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d00d6d9a339d Add linux-next specific files for 20180709
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17fdd90c400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=94fe2b586beccacd
dashboard link: https://syzkaller.appspot.com/bug?extid=3a0570f93c0d6ca388f5
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3a0570f93c0d6ca388f5@xxxxxxxxxxxxxxxxxxxxxxxxx

9pnet_virtio: no channels available for device (null)
Unknown ioctl 44801
9pnet_virtio: no channels available for device (null)
9pnet: Insufficient options for proto=fd
9pnet: Insufficient options for proto=fd
INFO: task syz-executor0:12044 blocked for more than 140 seconds.
      Not tainted 4.18.0-rc3-next-20180709+ #2
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D25408 12044   4539 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2853 [inline]
 __schedule+0x87c/0x1ed0 kernel/sched/core.c:3501
 schedule+0xfb/0x450 kernel/sched/core.c:3545
 __rwsem_down_write_failed_common+0x95d/0x1630  
kernel/locking/rwsem-xadd.c:566
 rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:595
 call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
 __down_write arch/x86/include/asm/rwsem.h:142 [inline]
 down_write+0xaa/0x130 kernel/locking/rwsem.c:72
 inode_lock include/linux/fs.h:748 [inline]
 utimes_common.isra.1+0x45c/0x8e0 fs/utimes.c:90
 do_utimes+0x1f7/0x380 fs/utimes.c:156
 do_futimesat+0x249/0x350 fs/utimes.c:212
 __do_sys_utimes fs/utimes.c:225 [inline]
 __se_sys_utimes fs/utimes.c:222 [inline]
 __x64_sys_utimes+0x59/0x80 fs/utimes.c:222
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455e29
Code: cc 64 48 8b 0c 25 f8 ff ff ff 48 3b 61 10 0f 86 ab 04 00 00 48 83 ec  
58 48 89 6c 24 50 48 8d 6c 24 50 48 8b 44 24 60 c6 00 00 <48> 8b 4c 24 68  
48 89 ca 48 89 50 08 48 8b 59 20 48 01 da 31 db 31
RSP: 002b:00007fac7c8b4c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000eb
RAX: ffffffffffffffda RBX: 00007fac7c8b56d4 RCX: 0000000000455e29
RDX: 0000000000000000 RSI: 0000000020000380 RDI: 0000000020000180
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c2af0 R14: 00000000004d4600 R15: 0000000000000002
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 898 Comm: khungtaskd Not tainted 4.18.0-rc3-next-20180709+ #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+0x1c9/0x2b4 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.5+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_all_cpu_backtrace include/linux/nmi.h:143 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
 watchdog+0xb39/0x10b0 kernel/hung_task.c:265
 kthread+0x345/0x410 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10  
arch/x86/include/asm/irqflags.h:54


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