Hello,
While running syzkaller fuzzer on f31494bd05b06b0cdb4da6aebe92eaafab970df6 (Aug 12), I've got the following deadlock report:
====================================================== [ INFO: possible circular locking dependency detected ] 4.8.0-rc1+ #11 Not tainted ------------------------------------------------------- syz-executor/7154 is trying to acquire lock: (register_mutex#5){+.+.+.}, at: [<ffffffff84fd6d4b>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341
but task is already holding lock: (&grp->list_mutex){++++.+}, at: [<ffffffff850138bb>] check_and_subscribe_port+0x5b/0x5c0 sound/core/seq/seq_ports.c:495
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&grp->list_mutex){++++.+}: [<ffffffff8147a3a8>] lock_acquire+0x208/0x430 kernel/locking/lockdep.c:3746 [<ffffffff863f6199>] down_read+0x49/0xc0 kernel/locking/rwsem.c:22 [< inline >] deliver_to_subscribers sound/core/seq/seq_clientmgr.c:681 [<ffffffff85005c5e>] snd_seq_deliver_event+0x35e/0x890 sound/core/seq/seq_clientmgr.c:822 [<ffffffff85006e96>] snd_seq_kernel_client_dispatch+0x126/0x170 sound/core/seq/seq_clientmgr.c:2418 [<ffffffff85012c52>] snd_seq_system_broadcast+0xb2/0xf0 sound/core/seq/seq_system.c:101 [<ffffffff84fff70a>] snd_seq_create_kernel_client+0x24a/0x330 sound/core/seq/seq_clientmgr.c:2297 [< inline >] snd_virmidi_dev_attach_seq sound/core/seq/seq_virmidi.c:383 [<ffffffff8502d29f>] snd_virmidi_dev_register+0x29f/0x750 sound/core/seq/seq_virmidi.c:450 [<ffffffff84fd208c>] snd_rawmidi_dev_register+0x30c/0xd40 sound/core/rawmidi.c:1645 [<ffffffff84f816d3>] __snd_device_register.part.0+0x63/0xc0 sound/core/device.c:164 [< inline >] __snd_device_register sound/core/device.c:162 [<ffffffff84f8235d>] snd_device_register_all+0xad/0x110 sound/core/device.c:212 [<ffffffff84f7546f>] snd_card_register+0xef/0x6c0 sound/core/init.c:749 [<ffffffff85040b7f>] snd_virmidi_probe+0x3ef/0x590 sound/drivers/virmidi.c:123 [<ffffffff833ebf7b>] platform_drv_probe+0x8b/0x170 drivers/base/platform.c:564 [< inline >] really_probe drivers/base/dd.c:377 [<ffffffff833e5993>] driver_probe_device+0x563/0xcc0 drivers/base/dd.c:499 [<ffffffff833e653d>] __device_attach_driver+0x21d/0x2e0 drivers/base/dd.c:594 [<ffffffff833df38f>] bus_for_each_drv+0x13f/0x1d0 drivers/base/bus.c:463 [<ffffffff833e51ef>] __device_attach+0x1ef/0x300 drivers/base/dd.c:651 [<ffffffff833e669a>] device_initial_probe+0x1a/0x20 drivers/base/dd.c:698 [<ffffffff833e2999>] bus_probe_device+0x1e9/0x290 drivers/base/bus.c:557 [<ffffffff833dc459>] device_add+0xc49/0x14c0 drivers/base/core.c:1120 [<ffffffff833eb629>] platform_device_add+0x2f9/0x7b0 drivers/base/platform.c:403 [<ffffffff833ed3b2>] platform_device_register_full+0x392/0x4b0 drivers/base/platform.c:536 [< inline >] platform_device_register_resndata ./include/linux/platform_device.h:111 [< inline >] platform_device_register_simple ./include/linux/platform_device.h:140 [<ffffffff8870fabd>] alsa_card_virmidi_init+0x104/0x1da sound/drivers/virmidi.c:172 [<ffffffff81002330>] do_one_initcall+0xa0/0x2b0 init/main.c:778 [< inline >] do_initcall_level init/main.c:843 [< inline >] do_initcalls init/main.c:851 [< inline >] do_basic_setup init/main.c:869 [<ffffffff88604d11>] kernel_init_freeable+0x47b/0x534 init/main.c:1016 [<ffffffff863e2f53>] kernel_init+0x13/0x180 init/main.c:942 [<ffffffff863fbdcf>] ret_from_fork+0x1f/0x40 arch/x86/entry/entry_64.S:393
-> #0 (register_mutex#5){+.+.+.}: [< inline >] check_prev_add kernel/locking/lockdep.c:1829 [< inline >] check_prevs_add kernel/locking/lockdep.c:1939 [< inline >] validate_chain kernel/locking/lockdep.c:2266 [<ffffffff814791f4>] __lock_acquire+0x4d44/0x4d80 kernel/locking/lockdep.c:3335 [<ffffffff8147a3a8>] lock_acquire+0x208/0x430 kernel/locking/lockdep.c:3746 [< inline >] __mutex_lock_common kernel/locking/mutex.c:521 [<ffffffff863f0ef1>] mutex_lock_nested+0xb1/0xa20 kernel/locking/mutex.c:621 [<ffffffff84fd6d4b>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341 [<ffffffff8502e7c7>] midisynth_subscribe+0xf7/0x350 sound/core/seq/seq_midi.c:188 [< inline >] subscribe_port sound/core/seq/seq_ports.c:427 [<ffffffff85013cc7>] check_and_subscribe_port+0x467/0x5c0 sound/core/seq/seq_ports.c:510 [<ffffffff85015da9>] snd_seq_port_connect+0x2c9/0x500 sound/core/seq/seq_ports.c:579 [<ffffffff850079b8>] snd_seq_ioctl_subscribe_port+0x1d8/0x2b0 sound/core/seq/seq_clientmgr.c:1480 [<ffffffff84ffe9e4>] snd_seq_do_ioctl+0x184/0x1e0 sound/core/seq/seq_clientmgr.c:2225 [<ffffffff84ffeae8>] snd_seq_kernel_client_ctl+0xa8/0x110 sound/core/seq/seq_clientmgr.c:2440 [<ffffffff85027664>] snd_seq_oss_midi_open+0x3b4/0x610 sound/core/seq/oss/seq_oss_midi.c:375 [<ffffffff85023d67>] snd_seq_oss_synth_setup_midi+0x107/0x4c0 sound/core/seq/oss/seq_oss_synth.c:281 [<ffffffff8501b0a8>] snd_seq_oss_open+0x748/0x8d0 sound/core/seq/oss/seq_oss_init.c:274 [<ffffffff85019d8a>] odev_open+0x6a/0x90 sound/core/seq/oss/seq_oss.c:138 [<ffffffff84f7040f>] soundcore_open+0x30f/0x640 sound/sound_core.c:639 [<ffffffff818069ea>] chrdev_open+0x22a/0x4c0 fs/char_dev.c:392 [<ffffffff817f146f>] do_dentry_open+0x69f/0xca0 fs/open.c:736 [<ffffffff817f4aa5>] vfs_open+0x105/0x220 fs/open.c:849 [< inline >] do_last fs/namei.c:3374 [<ffffffff8182c35d>] path_openat+0x1efd/0x2f60 fs/namei.c:3497 [<ffffffff81830b6e>] do_filp_open+0x18e/0x250 fs/namei.c:3532 [<ffffffff817f53c1>] do_sys_open+0x201/0x420 fs/open.c:1036 [< inline >] SYSC_open fs/open.c:1054 [<ffffffff817f560d>] SyS_open+0x2d/0x40 fs/open.c:1049 [<ffffffff863fbb80>] entry_SYSCALL_64_fastpath+0x23/0xc1 arch/x86/entry/entry_64.S:207
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&grp->list_mutex); lock(register_mutex#5); lock(&grp->list_mutex); lock(register_mutex#5);
*** DEADLOCK ***
2 locks held by syz-executor/7154: #0: (register_mutex#4){+.+.+.}, at: [<ffffffff85019d7f>] odev_open+0x5f/0x90 sound/core/seq/oss/seq_oss.c:137 #1: (&grp->list_mutex){++++.+}, at: [<ffffffff850138bb>] check_and_subscribe_port+0x5b/0x5c0 sound/core/seq/seq_ports.c:495
stack backtrace: CPU: 0 PID: 7154 Comm: syz-executor Not tainted 4.8.0-rc1+ #11 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffffffff878b7680 ffff880038b670f0 ffffffff82a5f719 ffffffff00000000 fffffbfff0f16ed0 ffffffff8901a0d0 ffffffff8901a0d0 ffffffff890191a0 ffff88003da2cf08 ffff88003da2c6c0 ffff880038b67140 ffffffff814708a8 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82a5f719>] dump_stack+0x12e/0x185 lib/dump_stack.c:51 [<ffffffff814708a8>] print_circular_bug+0x288/0x340 kernel/locking/lockdep.c:1202 [< inline >] check_prev_add kernel/locking/lockdep.c:1829 [< inline >] check_prevs_add kernel/locking/lockdep.c:1939 [< inline >] validate_chain kernel/locking/lockdep.c:2266 [<ffffffff814791f4>] __lock_acquire+0x4d44/0x4d80 kernel/locking/lockdep.c:3335 [<ffffffff8147a3a8>] lock_acquire+0x208/0x430 kernel/locking/lockdep.c:3746 [< inline >] __mutex_lock_common kernel/locking/mutex.c:521 [<ffffffff863f0ef1>] mutex_lock_nested+0xb1/0xa20 kernel/locking/mutex.c:621 [<ffffffff84fd6d4b>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341 [<ffffffff8502e7c7>] midisynth_subscribe+0xf7/0x350 sound/core/seq/seq_midi.c:188 [< inline >] subscribe_port sound/core/seq/seq_ports.c:427 [<ffffffff85013cc7>] check_and_subscribe_port+0x467/0x5c0 sound/core/seq/seq_ports.c:510 [<ffffffff85015da9>] snd_seq_port_connect+0x2c9/0x500 sound/core/seq/seq_ports.c:579 [<ffffffff850079b8>] snd_seq_ioctl_subscribe_port+0x1d8/0x2b0 sound/core/seq/seq_clientmgr.c:1480 [<ffffffff84ffe9e4>] snd_seq_do_ioctl+0x184/0x1e0 sound/core/seq/seq_clientmgr.c:2225 [<ffffffff84ffeae8>] snd_seq_kernel_client_ctl+0xa8/0x110 sound/core/seq/seq_clientmgr.c:2440 [<ffffffff85027664>] snd_seq_oss_midi_open+0x3b4/0x610 sound/core/seq/oss/seq_oss_midi.c:375 [<ffffffff85023d67>] snd_seq_oss_synth_setup_midi+0x107/0x4c0 sound/core/seq/oss/seq_oss_synth.c:281 [<ffffffff8501b0a8>] snd_seq_oss_open+0x748/0x8d0 sound/core/seq/oss/seq_oss_init.c:274 [<ffffffff85019d8a>] odev_open+0x6a/0x90 sound/core/seq/oss/seq_oss.c:138 [<ffffffff84f7040f>] soundcore_open+0x30f/0x640 sound/sound_core.c:639 [<ffffffff818069ea>] chrdev_open+0x22a/0x4c0 fs/char_dev.c:392 [<ffffffff817f146f>] do_dentry_open+0x69f/0xca0 fs/open.c:736 [<ffffffff817f4aa5>] vfs_open+0x105/0x220 fs/open.c:849 [< inline >] do_last fs/namei.c:3374 [<ffffffff8182c35d>] path_openat+0x1efd/0x2f60 fs/namei.c:3497 [<ffffffff81830b6e>] do_filp_open+0x18e/0x250 fs/namei.c:3532 [<ffffffff817f53c1>] do_sys_open+0x201/0x420 fs/open.c:1036 [< inline >] SYSC_open fs/open.c:1054 [<ffffffff817f560d>] SyS_open+0x2d/0x40 fs/open.c:1049 [<ffffffff863fbb80>] entry_SYSCALL_64_fastpath+0x23/0xc1 arch/x86/entry/entry_64.S:207