INFO: task hung in v9fs_file_fsync_dotl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 0854ba5ff5c9 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17eb36e6400000
kernel config: https://syzkaller.appspot.com/x/.config?x=88e9a8a39dc0be2d
dashboard link: https://syzkaller.appspot.com/bug?extid=9454d1f8a38ceccecc63
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [asma...@codewreck.org eri...@gmail.com
linux-...@vger.kernel.org lu...@ionkov.net
v9fs-de...@lists.sourceforge.net]

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+9454d1...@syzkaller.appspotmail.com

syz-executor4 (8943) used greatest stack depth: 12256 bytes left
INFO: task syz-executor1:8963 blocked for more than 140 seconds.
Not tainted 4.19.0-rc7+ #51
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1 D25400 8963 5812 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2825 [inline]
__schedule+0x86c/0x1ed0 kernel/sched/core.c:3473
schedule+0xfe/0x460 kernel/sched/core.c:3517
__rwsem_down_write_failed_common+0xbb9/0x1670
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+0xa5/0x130 kernel/locking/rwsem.c:72
inode_lock include/linux/fs.h:738 [inline]
v9fs_file_fsync_dotl+0xb6/0x120 fs/9p/vfs_file.c:475
vfs_fsync_range+0x140/0x220 fs/sync.c:197
vfs_fsync fs/sync.c:211 [inline]
do_fsync+0x52/0xa0 fs/sync.c:221
__do_sys_fdatasync fs/sync.c:234 [inline]
__se_sys_fdatasync fs/sync.c:232 [inline]
__x64_sys_fdatasync+0x36/0x50 fs/sync.c:232
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457579
Code: 24 08 48 89 01 e8 d7 2d fc ff e8 22 7a fc ff b8 02 00 00 00 48 8d 0d
6a 60 09 01 87 01 8b 05 62 60 09 01 83 f8 01 0f 85 8a 00 <00> 00 b8 01 00
00 00 88 05 9e 65 09 01 84 c0 74 72 b8 01 00 00 00
RSP: 002b:00007fd56799ec78 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000457579
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd56799f6d4
R13: 00000000004bdd86 R14: 00000000004ccad8 R15: 00000000ffffffff
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 985 Comm: khungtaskd Not tainted 4.19.0-rc7+ #51
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+0x1c4/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.3+0x63/0xa2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b3/0x1ed 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:144 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
watchdog+0xb3e/0x1050 kernel/hung_task.c:265
kthread+0x35a/0x420 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413
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:57


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.