Hello,
While running syzkaller fuzzer I've got the following lockdep report:
====================================================== [ INFO: possible circular locking dependency detected ] 4.4.0+ #276 Not tainted ------------------------------------------------------- syz-executor/21025 is trying to acquire lock: (register_mutex#5){+.+.+.}, at: [<ffffffff84f889cb>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341
but task is already holding lock: (&grp->list_mutex/1){+.+...}, at: [<ffffffff84fc4afa>] snd_seq_port_connect+0x1ba/0x840 sound/core/seq/seq_ports.c:506
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&grp->list_mutex/1){+.+...}: [<ffffffff8145ad8c>] lock_acquire+0x1dc/0x430 kernel/locking/lockdep.c:3585 [<ffffffff8144851a>] down_write_nested+0x4a/0xa0 kernel/locking/rwsem.c:149 [<ffffffff84fc4afa>] snd_seq_port_connect+0x1ba/0x840 sound/core/seq/seq_ports.c:506 [<ffffffff84fb6f54>] snd_seq_ioctl_subscribe_port+0x1c4/0x290 sound/core/seq/seq_clientmgr.c:1464 [<ffffffff84fb126d>] snd_seq_do_ioctl+0x19d/0x1c0 sound/core/seq/seq_clientmgr.c:2209 [<ffffffff84fb2c2b>] snd_seq_kernel_client_ctl+0xdb/0x170 sound/core/seq/seq_clientmgr.c:2423 [<ffffffff88413c20>] snd_seq_oss_create_client+0x253/0x2d5 sound/core/seq/oss/seq_oss_init.c:119 [<ffffffff8841393e>] alsa_seq_oss_init+0x1af/0x23e sound/core/seq/oss/seq_oss.c:89 [<ffffffff81002259>] do_one_initcall+0x159/0x380 init/main.c:794 [< inline >] do_initcall_level init/main.c:859 [< inline >] do_initcalls init/main.c:867 [< inline >] do_basic_setup init/main.c:885 [<ffffffff88315c1a>] kernel_init_freeable+0x474/0x52d init/main.c:1010 [<ffffffff86312683>] kernel_init+0x13/0x150 init/main.c:936 [<ffffffff86336fef>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
-> #1 (&grp->list_mutex){++++.+}: [<ffffffff8145ad8c>] lock_acquire+0x1dc/0x430 kernel/locking/lockdep.c:3585 [<ffffffff863323a7>] down_read+0x47/0x60 kernel/locking/rwsem.c:22 [< inline >] deliver_to_subscribers sound/core/seq/seq_clientmgr.c:679 [<ffffffff84fb5509>] snd_seq_deliver_event+0x5a9/0x800 sound/core/seq/seq_clientmgr.c:817 [<ffffffff84fb6466>] snd_seq_kernel_client_dispatch+0x126/0x170 sound/core/seq/seq_clientmgr.c:2401 [<ffffffff84fc1e62>] snd_seq_system_broadcast+0xb2/0xf0 sound/core/seq/seq_system.c:101 [<ffffffff84fb248e>] snd_seq_create_kernel_client+0x21e/0x300 sound/core/seq/seq_clientmgr.c:2280 [< inline >] snd_virmidi_dev_attach_seq sound/core/seq/seq_virmidi.c:372 [<ffffffff84fdc55f>] snd_virmidi_dev_register+0x29f/0x750 sound/core/seq/seq_virmidi.c:439 [<ffffffff84f824ec>] snd_rawmidi_dev_register+0x30c/0xd40 sound/core/rawmidi.c:1589 [<ffffffff84f33583>] __snd_device_register.part.0+0x63/0xc0 sound/core/device.c:164 [< inline >] __snd_device_register sound/core/device.c:162 [<ffffffff84f341ed>] snd_device_register_all+0xad/0x110 sound/core/device.c:212 [<ffffffff84f277cf>] snd_card_register+0xef/0x6a0 sound/core/init.c:749 [<ffffffff84fefc0f>] snd_virmidi_probe+0x3ef/0x590 sound/drivers/virmidi.c:123 [<ffffffff832feb6c>] platform_drv_probe+0x8c/0x160 drivers/base/platform.c:562 [< inline >] really_probe drivers/base/dd.c:377 [<ffffffff832f862e>] driver_probe_device+0x37e/0xc90 drivers/base/dd.c:499 [<ffffffff832f926e>] __device_attach_driver+0x19e/0x250 drivers/base/dd.c:584 [<ffffffff832f23df>] bus_for_each_drv+0x13f/0x1d0 drivers/base/bus.c:464 [<ffffffff832f809f>] __device_attach+0x1ef/0x2e0 drivers/base/dd.c:641 [<ffffffff832f93ba>] device_initial_probe+0x1a/0x20 drivers/base/dd.c:688 [<ffffffff832f5939>] bus_probe_device+0x1e9/0x290 drivers/base/bus.c:558 [<ffffffff832ef11b>] device_add+0x84b/0x1490 drivers/base/core.c:1120 [<ffffffff832fe2c9>] platform_device_add+0x389/0x790 drivers/base/platform.c:403 [<ffffffff832fff26>] platform_device_register_full+0x396/0x4c0 drivers/base/platform.c:535 [< inline >] platform_device_register_resndata include/linux/platform_device.h:111 [< inline >] platform_device_register_simple include/linux/platform_device.h:140 [<ffffffff884146d1>] alsa_card_virmidi_init+0x104/0x1da sound/drivers/virmidi.c:172 [<ffffffff81002259>] do_one_initcall+0x159/0x380 init/main.c:794 [< inline >] do_initcall_level init/main.c:859 [< inline >] do_initcalls init/main.c:867 [< inline >] do_basic_setup init/main.c:885 [<ffffffff88315c1a>] kernel_init_freeable+0x474/0x52d init/main.c:1010 [<ffffffff86312683>] kernel_init+0x13/0x150 init/main.c:936 [<ffffffff86336fef>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
-> #0 (register_mutex#5){+.+.+.}: [< inline >] check_prev_add kernel/locking/lockdep.c:1853 [< inline >] check_prevs_add kernel/locking/lockdep.c:1958 [< inline >] validate_chain kernel/locking/lockdep.c:2144 [<ffffffff8145742b>] __lock_acquire+0x31eb/0x4700 kernel/locking/lockdep.c:3206 [<ffffffff8145ad8c>] lock_acquire+0x1dc/0x430 kernel/locking/lockdep.c:3585 [< inline >] __mutex_lock_common kernel/locking/mutex.c:518 [<ffffffff8632cf61>] mutex_lock_nested+0xb1/0xa50 kernel/locking/mutex.c:618 [<ffffffff84f889cb>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341 [<ffffffff84fdda77>] midisynth_subscribe+0xf7/0x340 sound/core/seq/seq_midi.c:188 [<ffffffff84fc2a4e>] subscribe_port.isra.2+0x14e/0x2b0 sound/core/seq/seq_ports.c:426 [<ffffffff84fc4dd0>] snd_seq_port_connect+0x490/0x840 sound/core/seq/seq_ports.c:527 [<ffffffff84fb6f54>] snd_seq_ioctl_subscribe_port+0x1c4/0x290 sound/core/seq/seq_clientmgr.c:1464 [<ffffffff84fb126d>] snd_seq_do_ioctl+0x19d/0x1c0 sound/core/seq/seq_clientmgr.c:2209 [<ffffffff84fb2c2b>] snd_seq_kernel_client_ctl+0xdb/0x170 sound/core/seq/seq_clientmgr.c:2423 [<ffffffff84fd69e4>] snd_seq_oss_midi_open+0x3b4/0x610 sound/core/seq/oss/seq_oss_midi.c:375 [<ffffffff84fd6ccb>] snd_seq_oss_midi_open_all+0x8b/0xd0 sound/core/seq/oss/seq_oss_midi.c:306 [<ffffffff84fca1d5>] snd_seq_oss_open+0x5c5/0x8d0 sound/core/seq/oss/seq_oss_init.c:276 [<ffffffff84fc903a>] odev_open+0x6a/0x90 sound/core/seq/oss/seq_oss.c:138 [<ffffffff84f2279f>] soundcore_open+0x30f/0x640 sound/sound_core.c:639 [<ffffffff817be1fa>] chrdev_open+0x22a/0x4c0 fs/char_dev.c:388 [<ffffffff817a9c02>] do_dentry_open+0x6a2/0xcb0 fs/open.c:736 [<ffffffff817ad2db>] vfs_open+0x17b/0x1f0 fs/open.c:853 [< inline >] do_last fs/namei.c:3254 [<ffffffff817e00d9>] path_openat+0xde9/0x5e30 fs/namei.c:3386 [<ffffffff817e895e>] do_filp_open+0x18e/0x250 fs/namei.c:3421 [<ffffffff817ada5c>] do_sys_open+0x1fc/0x420 fs/open.c:1022 [< inline >] SYSC_open fs/open.c:1040 [<ffffffff817adcad>] SyS_open+0x2d/0x40 fs/open.c:1035 [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185
other info that might help us debug this:
Chain exists of: register_mutex#5 --> &grp->list_mutex --> &grp->list_mutex/1
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&grp->list_mutex/1); lock(&grp->list_mutex); lock(&grp->list_mutex/1); lock(register_mutex#5);
*** DEADLOCK ***
3 locks held by syz-executor/21025: #0: (register_mutex#4){+.+.+.}, at: [<ffffffff84fc902f>] odev_open+0x5f/0x90 sound/core/seq/oss/seq_oss.c:137 #1: (&grp->list_mutex){++++.+}, at: [<ffffffff84fc4ae2>] snd_seq_port_connect+0x1a2/0x840 sound/core/seq/seq_ports.c:505 #2: (&grp->list_mutex/1){+.+...}, at: [<ffffffff84fc4afa>] snd_seq_port_connect+0x1ba/0x840 sound/core/seq/seq_ports.c:506
stack backtrace: CPU: 2 PID: 21025 Comm: syz-executor Not tainted 4.4.0+ #276 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 00000000ffffffff ffff88006d0af0c0 ffffffff82999e2d ffffffff88fa1eb0 ffffffff88fa2f90 ffffffff88fa2060 ffff88006d0af110 ffffffff81450658 ffff880065c8df00 ffff880065c8e79a 0000000000000000 ffff880065c8e778 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50 [<ffffffff81450658>] print_circular_bug+0x288/0x340 kernel/locking/lockdep.c:1226 [< inline >] check_prev_add kernel/locking/lockdep.c:1853 [< inline >] check_prevs_add kernel/locking/lockdep.c:1958 [< inline >] validate_chain kernel/locking/lockdep.c:2144 [<ffffffff8145742b>] __lock_acquire+0x31eb/0x4700 kernel/locking/lockdep.c:3206 [<ffffffff8145ad8c>] lock_acquire+0x1dc/0x430 kernel/locking/lockdep.c:3585 [< inline >] __mutex_lock_common kernel/locking/mutex.c:518 [<ffffffff8632cf61>] mutex_lock_nested+0xb1/0xa50 kernel/locking/mutex.c:618 [<ffffffff84f889cb>] snd_rawmidi_kernel_open+0x4b/0x260 sound/core/rawmidi.c:341 [<ffffffff84fdda77>] midisynth_subscribe+0xf7/0x340 sound/core/seq/seq_midi.c:188 [<ffffffff84fc2a4e>] subscribe_port.isra.2+0x14e/0x2b0 sound/core/seq/seq_ports.c:426 [<ffffffff84fc4dd0>] snd_seq_port_connect+0x490/0x840 sound/core/seq/seq_ports.c:527 [<ffffffff84fb6f54>] snd_seq_ioctl_subscribe_port+0x1c4/0x290 sound/core/seq/seq_clientmgr.c:1464 [<ffffffff84fb126d>] snd_seq_do_ioctl+0x19d/0x1c0 sound/core/seq/seq_clientmgr.c:2209 [<ffffffff84fb2c2b>] snd_seq_kernel_client_ctl+0xdb/0x170 sound/core/seq/seq_clientmgr.c:2423 [<ffffffff84fd69e4>] snd_seq_oss_midi_open+0x3b4/0x610 sound/core/seq/oss/seq_oss_midi.c:375 [<ffffffff84fd6ccb>] snd_seq_oss_midi_open_all+0x8b/0xd0 sound/core/seq/oss/seq_oss_midi.c:306 [<ffffffff84fca1d5>] snd_seq_oss_open+0x5c5/0x8d0 sound/core/seq/oss/seq_oss_init.c:276 [<ffffffff84fc903a>] odev_open+0x6a/0x90 sound/core/seq/oss/seq_oss.c:138 [<ffffffff84f2279f>] soundcore_open+0x30f/0x640 sound/sound_core.c:639 [<ffffffff817be1fa>] chrdev_open+0x22a/0x4c0 fs/char_dev.c:388 [<ffffffff817a9c02>] do_dentry_open+0x6a2/0xcb0 fs/open.c:736 [<ffffffff817ad2db>] vfs_open+0x17b/0x1f0 fs/open.c:853 [< inline >] do_last fs/namei.c:3254 [<ffffffff817e00d9>] path_openat+0xde9/0x5e30 fs/namei.c:3386 [<ffffffff817e895e>] do_filp_open+0x18e/0x250 fs/namei.c:3421 [<ffffffff817ada5c>] do_sys_open+0x1fc/0x420 fs/open.c:1022 [< inline >] SYSC_open fs/open.c:1040 [<ffffffff817adcad>] SyS_open+0x2d/0x40 fs/open.c:1035 [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185
On commit 30f05309bde49295e02e45c7e615f73aa4e0ccc2.