INFO: task hung in vfs_setxattr

[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=1414611c400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=94fe2b586beccacd
dashboard link: https://syzkaller.appspot.com/bug?extid=6cd4d2845f652967921c
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+6cd4d2845f652967921c@xxxxxxxxxxxxxxxxxxxxxxxxx

FAT-fs (loop6): Unrecognized mount option "uid=" or missing value
INFO: task syz-executor3:28571 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-executor3   D25408 28571   4477 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]
 vfs_setxattr+0x96/0x100 fs/xattr.c:218
 setxattr+0x2ea/0x450 fs/xattr.c:450
 path_setxattr+0x1e3/0x230 fs/xattr.c:469
 __do_sys_setxattr fs/xattr.c:484 [inline]
 __se_sys_setxattr fs/xattr.c:480 [inline]
 __x64_sys_setxattr+0xc4/0x150 fs/xattr.c:480
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455e29
Code: Bad RIP value.
RSP: 002b:00007f1c60d88c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000bc
RAX: ffffffffffffffda RBX: 00007f1c60d896d4 RCX: 0000000000455e29
RDX: 0000000020000400 RSI: 0000000020000380 RDI: 0000000020000140
RBP: 000000000072bff0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004bbff8 R14: 00000000004d3370 R15: 0000000000000002
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 897 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
CPU: 0 PID: 2419 Comm: udevd Not tainted 4.18.0-rc3-next-20180709+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0033:0x4043d1
Code: d5 b0 00 00 bf a0 54 62 00 e8 9b fb 00 00 bf b0 54 62 00 e8 91 fb 00  
00 44 89 7c 24 64 4c 89 6c 24 50 49 89 df 44 89 74 24 58 <80> 3d b0 11 22  
00 00 0f 84 88 07 00 00 83 7c 24 58 00 78 1e 8b 54
RSP: 002b:00007ffee90bf370 EFLAGS: 00000246
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 00007ffee90bf46c
RDX: 0000000000000004 RSI: 0000000000000001 RDI: 00000000006254a0
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000008 R11: 0000000000000004 R12: 0000000000000003
R13: 0000000000000000 R14: 0000000000891520 R15: 0000000000883250
FS:  00007f96fedce7a0(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 00000001ca6fa000 CR4: 00000000001406f0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600


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