Re: [syzbot] [input?] possible deadlock in __kernfs_remove (3)
From: syzbot <hidden>
Date: 2026-08-29 21:22:31
Also in:
driver-core, lkml, netdev
syzbot has found a reproducer for the following issue on: HEAD commit: cf72cbb39da8 Merge tag 'io_uring-7.3-20260828' of git://gi.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=14c09d79580000 kernel config: https://syzkaller.appspot.com/x/.config?x=85bc5cc2fc7394d9 dashboard link: https://syzkaller.appspot.com/bug?extid=1075f6dc93f398c1857e compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 userspace arch: i386 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=161fae25580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1084c379580000 Downloadable assets: disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-cf72cbb3.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/755d053ff703/vmlinux-cf72cbb3.xz kernel image: https://storage.googleapis.com/syzbot-assets/0837738ba281/bzImage-cf72cbb3.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+1075f6dc93f398c1857e@syzkaller.appspotmail.com ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.0.17/6098 is trying to acquire lock: ffff88804e56bf08 (kn->active#66){++++}-{0:0}, at: __kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579 but task is already holding lock: ffffffff904e2360 (serio_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline] ffffffff904e2360 (serio_mutex){+.+.}-{4:4}, at: serio_unregister_port+0x1b/0x40 drivers/input/serio/serio.c:677 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (serio_mutex){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5908 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821 class_mutex_intr_constructor include/linux/mutex.h:255 [inline] drvctl_store+0x3c/0x350 drivers/input/serio/serio.c:360 dev_attr_store+0x58/0x80 drivers/base/core.c:2509 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6af/0x1050 fs/read_write.c:687 ksys_write+0x12a/0x250 fs/read_write.c:739 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline] __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316 entry_SYSENTER_compat_after_hwframe+0x84/0x8e -> #0 (kn->active#66){++++}-{0:0}: check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181 check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254 lock_acquire kernel/locking/lockdep.c:5908 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865 kernfs_drain+0x4f0/0x600 fs/kernfs/dir.c:532 __kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579 kernfs_remove_by_name_ns+0x7c/0x120 fs/kernfs/dir.c:1797 kernfs_remove_by_name include/linux/kernfs.h:644 [inline] remove_files+0x96/0x1c0 fs/sysfs/group.c:28 sysfs_remove_group+0x8b/0x1b0 fs/sysfs/group.c:328 sysfs_remove_groups fs/sysfs/group.c:352 [inline] sysfs_remove_groups+0x60/0xb0 fs/sysfs/group.c:344 device_remove_groups drivers/base/core.c:2918 [inline] device_remove_attrs+0x192/0x290 drivers/base/core.c:3048 device_del+0x36e/0x9b0 drivers/base/core.c:3964 serio_destroy_port+0x476/0x590 drivers/input/serio/serio.c:543 serio_unregister_port+0x2b/0x40 drivers/input/serio/serio.c:680 userio_char_release+0x91/0xe0 drivers/input/serio/userio.c:105 __fput+0x3ff/0xb50 fs/file_table.c:512 task_work_run+0x150/0x240 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:70 [inline] exit_to_user_mode_loop+0x1d8/0x700 kernel/entry/common.c:101 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:336 [inline] __do_fast_syscall_32+0x59f/0x8b0 arch/x86/entry/syscall_32.c:294 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316 entry_SYSENTER_compat_after_hwframe+0x84/0x8e other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(serio_mutex); lock(kn->active#66); lock(serio_mutex); lock(kn->active#66); *** DEADLOCK *** locks held by syz.0.17/6098: 1, last CPU#2: #0: ffffffff904e2360 (serio_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline] #0: ffffffff904e2360 (serio_mutex){+.+.}-{4:4}, at: serio_unregister_port+0x1b/0x40 drivers/input/serio/serio.c:677 stack backtrace: CPU: 2 UID: 0 PID: 6098 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181 check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254 lock_acquire kernel/locking/lockdep.c:5908 [inline] lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865 kernfs_drain+0x4f0/0x600 fs/kernfs/dir.c:532 __kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579 kernfs_remove_by_name_ns+0x7c/0x120 fs/kernfs/dir.c:1797 kernfs_remove_by_name include/linux/kernfs.h:644 [inline] remove_files+0x96/0x1c0 fs/sysfs/group.c:28 sysfs_remove_group+0x8b/0x1b0 fs/sysfs/group.c:328 sysfs_remove_groups fs/sysfs/group.c:352 [inline] sysfs_remove_groups+0x60/0xb0 fs/sysfs/group.c:344 device_remove_groups drivers/base/core.c:2918 [inline] device_remove_attrs+0x192/0x290 drivers/base/core.c:3048 device_del+0x36e/0x9b0 drivers/base/core.c:3964 serio_destroy_port+0x476/0x590 drivers/input/serio/serio.c:543 serio_unregister_port+0x2b/0x40 drivers/input/serio/serio.c:680 userio_char_release+0x91/0xe0 drivers/input/serio/userio.c:105 __fput+0x3ff/0xb50 fs/file_table.c:512 task_work_run+0x150/0x240 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:70 [inline] exit_to_user_mode_loop+0x1d8/0x700 kernel/entry/common.c:101 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:336 [inline] __do_fast_syscall_32+0x59f/0x8b0 arch/x86/entry/syscall_32.c:294 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316 entry_SYSENTER_compat_after_hwframe+0x84/0x8e RIP: 0023:0xf6ffefec Code: Unable to access opcode bytes at 0xf6ffefc2. RSP: 002b:00000000ffbd8fbc EFLAGS: 00000202 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 0000000000000003 RCX: 000000000000001e RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 </TASK> --- If you want syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing.