====================================================== WARNING: possible circular locking dependency detected 6.14.0-rc7-syzkaller #0 Not tainted ------------------------------------------------------ syz.0.488/8394 is trying to acquire lock: ffff888028e09fe0 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault mm/memory.c:6839 [inline] ffff888028e09fe0 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0xe3/0x190 mm/memory.c:6832 but task is already holding lock: ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:201 [inline] ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: snd_timer_user_next_device sound/core/timer.c:1526 [inline] ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: __snd_timer_user_ioctl.isra.0+0xa0c/0x2640 sound/core/timer.c:2247 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (register_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730 snd_timer_open+0x90/0x1020 sound/core/timer.c:307 loopback_snd_timer_open+0xaca/0x1020 sound/drivers/aloop.c:1202 loopback_open+0x2bf/0x13a0 sound/drivers/aloop.c:1268 snd_pcm_open_substream+0xa50/0x17c0 sound/core/pcm_native.c:2753 snd_pcm_oss_open_file sound/core/oss/pcm_oss.c:2439 [inline] snd_pcm_oss_open+0x754/0x1400 sound/core/oss/pcm_oss.c:2520 soundcore_open+0x409/0x580 sound/sound_core.c:594 chrdev_open+0x237/0x6a0 fs/char_dev.c:414 do_dentry_open+0x735/0x1c40 fs/open.c:956 vfs_open+0x82/0x3f0 fs/open.c:1086 do_open fs/namei.c:3830 [inline] path_openat+0x1e88/0x2d80 fs/namei.c:3989 do_filp_open+0x20c/0x470 fs/namei.c:4016 do_sys_openat2+0x17a/0x1e0 fs/open.c:1428 do_sys_open fs/open.c:1443 [inline] __do_sys_openat fs/open.c:1459 [inline] __se_sys_openat fs/open.c:1454 [inline] __x64_sys_openat+0x175/0x210 fs/open.c:1454 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&loopback->cable_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730 rule_format+0x111/0x3b0 sound/drivers/aloop.c:982 constrain_params_by_rules+0x547/0xca0 sound/core/pcm_native.c:436 snd_pcm_hw_refine sound/core/pcm_native.c:567 [inline] snd_pcm_hw_refine+0x7e8/0xad0 sound/core/pcm_native.c:545 snd_pcm_hw_param_mask sound/core/oss/pcm_oss.c:190 [inline] snd_pcm_oss_change_params_locked+0x645/0x3a60 sound/core/oss/pcm_oss.c:886 snd_pcm_oss_change_params sound/core/oss/pcm_oss.c:1105 [inline] snd_pcm_oss_mmap+0x603/0x7c0 sound/core/oss/pcm_oss.c:2914 call_mmap include/linux/fs.h:2245 [inline] mmap_file mm/internal.h:124 [inline] __mmap_new_file_vma mm/vma.c:2296 [inline] __mmap_new_vma mm/vma.c:2360 [inline] __mmap_region+0x181f/0x2760 mm/vma.c:2461 mmap_region+0x1ab/0x3f0 mm/vma.c:2539 do_mmap+0xd8d/0x11b0 mm/mmap.c:561 vm_mmap_pgoff+0x279/0x440 mm/util.c:578 ksys_mmap_pgoff+0x32c/0x5c0 mm/mmap.c:607 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline] __se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline] __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&mm->mmap_lock){++++}-{4:4}: check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain kernel/locking/lockdep.c:3906 [inline] __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851 __might_fault mm/memory.c:6839 [inline] __might_fault+0x11b/0x190 mm/memory.c:6832 _inline_copy_to_user include/linux/uaccess.h:192 [inline] _copy_to_user+0x2d/0xd0 lib/usercopy.c:26 copy_to_user include/linux/uaccess.h:225 [inline] snd_timer_user_gstatus sound/core/timer.c:1699 [inline] __snd_timer_user_ioctl.isra.0+0xd47/0x2640 sound/core/timer.c:2256 snd_timer_user_ioctl+0x72/0xb0 sound/core/timer.c:2291 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl fs/ioctl.c:892 [inline] __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &mm->mmap_lock --> &loopback->cable_lock --> register_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(register_mutex); lock(&loopback->cable_lock); lock(register_mutex); rlock(&mm->mmap_lock); *** DEADLOCK *** 2 locks held by syz.0.488/8394: #0: ffff8880332c2568 (&tu->ioctl_lock){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:201 [inline] #0: ffff8880332c2568 (&tu->ioctl_lock){+.+.}-{4:4}, at: snd_timer_user_ioctl+0x4a/0xb0 sound/core/timer.c:2290 #1: ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:201 [inline] #1: ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: snd_timer_user_next_device sound/core/timer.c:1526 [inline] #1: ffffffff8fdaf688 (register_mutex){+.+.}-{4:4}, at: __snd_timer_user_ioctl.isra.0+0xa0c/0x2640 sound/core/timer.c:2247 stack backtrace: CPU: 1 UID: 0 PID: 8394 Comm: syz.0.488 Not tainted 6.14.0-rc7-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208 check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain kernel/locking/lockdep.c:3906 [inline] __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851 __might_fault mm/memory.c:6839 [inline] __might_fault+0x11b/0x190 mm/memory.c:6832 _inline_copy_to_user include/linux/uaccess.h:192 [inline] _copy_to_user+0x2d/0xd0 lib/usercopy.c:26 copy_to_user include/linux/uaccess.h:225 [inline] snd_timer_user_gstatus sound/core/timer.c:1699 [inline] __snd_timer_user_ioctl.isra.0+0xd47/0x2640 sound/core/timer.c:2256 snd_timer_user_ioctl+0x72/0xb0 sound/core/timer.c:2291 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl fs/ioctl.c:892 [inline] __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fdbb2f8d169 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fdbb3d93038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fdbb31a6080 RCX: 00007fdbb2f8d169 RDX: 0000400000000140 RSI: 00000000c0145401 RDI: 0000000000000003 RBP: 00007fdbb300e2a0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007fdbb31a6080 R15: 00007ffee7e06528