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SubjectINFO: task hung in snd_seq_kernel_client_ctl
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Hello,

syzbot found the following crash on:

HEAD commit: 2f4c4d83 Add linux-next specific files for 20190411
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1261f42d200000
kernel config: https://syzkaller.appspot.com/x/.config?x=bfc6a0294e6babef
dashboard link: https://syzkaller.appspot.com/bug?extid=47ded6c0f23016cde310
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=130cecb7200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13c0efab200000

The bug was bisected to:

commit feb689025fbb6f0aa6297d3ddf97de945ea4ad32
Author: Takashi Iwai <tiwai@suse.de>
Date: Tue Apr 9 15:35:22 2019 +0000

ALSA: seq: Protect in-kernel ioctl calls with mutex

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=178552b7200000
final crash: https://syzkaller.appspot.com/x/report.txt?x=144552b7200000
console output: https://syzkaller.appspot.com/x/log.txt?x=104552b7200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+47ded6c0f23016cde310@syzkaller.appspotmail.com
Fixes: feb689025fbb ("ALSA: seq: Protect in-kernel ioctl calls with mutex")

INFO: task syz-executor971:9265 blocked for more than 143 seconds.
Not tainted 5.1.0-rc4-next-20190411 #23
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor971 D28264 9265 9263 0x80000002
Call Trace:
context_switch kernel/sched/core.c:2877 [inline]
__schedule+0x817/0x1cc0 kernel/sched/core.c:3518
schedule+0x92/0x180 kernel/sched/core.c:3562
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3620
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1310 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
snd_seq_kernel_client_ctl+0xe5/0x170 sound/core/seq/seq_clientmgr.c:2345
snd_seq_oss_control sound/core/seq/oss/seq_oss_device.h:157 [inline]
snd_seq_oss_writeq_clear+0xe0/0x140 sound/core/seq/oss/seq_oss_writeq.c:85
snd_seq_oss_writeq_delete+0x20/0x40 sound/core/seq/oss/seq_oss_writeq.c:69
free_devinfo+0x66/0xc0 sound/core/seq/oss/seq_oss_init.c:406
port_delete+0xe8/0x1c0 sound/core/seq/seq_ports.c:272
snd_seq_delete_port+0x266/0x330 sound/core/seq/seq_ports.c:301
snd_seq_ioctl_delete_port+0xba/0x190 sound/core/seq/seq_clientmgr.c:1321
snd_seq_kernel_client_ctl+0x112/0x170 sound/core/seq/seq_clientmgr.c:2346
snd_seq_event_port_detach+0xba/0x100 sound/core/seq/seq_ports.c:705
delete_port+0x87/0xd0 sound/core/seq/oss/seq_oss_init.c:354
snd_seq_oss_release+0xf5/0x150 sound/core/seq/oss/seq_oss_init.c:433
odev_release+0x54/0x80 sound/core/seq/oss/seq_oss.c:153
__fput+0x2e5/0x8d0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x14a/0x1c0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x90a/0x2fa0 kernel/exit.c:876
do_group_exit+0x135/0x370 kernel/exit.c:980
__do_sys_exit_group kernel/exit.c:991 [inline]
__se_sys_exit_group kernel/exit.c:989 [inline]
__x64_sys_exit_group+0x44/0x50 kernel/exit.c:989
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x43ed98
Code: Bad RIP value.
RSP: 002b:00007fff4f4de2a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ed98
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004be5a8 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d0180 R14: 0000000000000000 R15: 0000000000000000
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 1038 Comm: khungtaskd Not tainted 5.1.0-rc4-next-20190411 #23
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+0x172/0x1f0 lib/dump_stack.c:113
nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1be/0x236 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:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
watchdog+0x9b7/0xec0 kernel/hung_task.c:288
kthread+0x357/0x430 kernel/kthread.c:254
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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