INFO: task hung in ucma_close

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1c34981993da Add linux-next specific files for 20180719
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=147bcf94400000
kernel config: https://syzkaller.appspot.com/x/.config?x=7002497517b09aec
dashboard link: https://syzkaller.appspot.com/bug?extid=6e1c3cc49b13643124fa
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [dasaratharama...@intel.com dled...@redhat.com
j...@ziepe.ca le...@kernel.org linux-...@vger.kernel.org
linux...@vger.kernel.org pa...@mellanox.com rol...@purestorage.com
sean....@intel.com]

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+6e1c3c...@syzkaller.appspotmail.com

INFO: task syz-executor5:20647 blocked for more than 140 seconds.
Not tainted 4.18.0-rc5-next-20180719+ #11
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor5 D24816 20647 4443 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2821 [inline]
__schedule+0x87c/0x1ea0 kernel/sched/core.c:3469
schedule+0xfb/0x450 kernel/sched/core.c:3513
schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3571
__mutex_lock_common kernel/locking/mutex.c:1003 [inline]
__mutex_lock+0xbf5/0x1680 kernel/locking/mutex.c:1073
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
ucma_close+0x4c/0x300 drivers/infiniband/core/ucma.c:1739
__fput+0x376/0x8a0 fs/file_table.c:279
____fput+0x15/0x20 fs/file_table.c:312
task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x40fb91
Code: 4a 00 48 89 04 24 48 c7 44 24 08 11 00 00 00 e8 55 bd 01 00 0f 0b e8
ce a3 04 00 e9 59 ff ff ff cc cc cc cc cc cc cc cc cc 64 <48> 8b 0c 25 f8
ff ff ff 48 8d 44 24 e0 48 3b 41 10 0f 86 0f 05 00
RSP: 002b:00007ffd325ed0e0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000016 RCX: 000000000040fb91
RDX: 0000000000000000 RSI: 00000000007306f8 RDI: 0000000000000015
RBP: 0000000000000013 R08: 0000000000000000 R09: 0000000000000000
R10: 00007ffd325ecf60 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000000 R14: 00007ffd325ed790 R15: 00000000007034c0
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 903 Comm: khungtaskd Not tainted 4.18.0-rc5-next-20180719+ #11
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.3+0x48/0x88 lib/nmi_backtrace.c:101
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:144 [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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[syzbot]

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