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:

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