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2002:a05:6820:4d4b:10b0:67b:deec:1435 with SMTP id 006d021491bc7-67bdeec178emr50666eaf.21.1773371309960; Thu, 12 Mar 2026 20:08:29 -0700 (PDT) Date: Thu, 12 Mar 2026 20:08:29 -0700 In-Reply-To: <000000000000dd477c0600d6d815@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <69b37fad.a00a0220.3b25d1.0005.GAE@google.com> Subject: Re: [syzbot] [kernfs?] possible deadlock in lookup_slow (3) From: syzbot To: driver-core@lists.linux.dev, gregkh@linuxfoundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tj@kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable syzbot has found a reproducer for the following issue on: HEAD commit: 8004279c41ad Merge tag 'nfs-for-7.0-2' of git://git.linux-.= . git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=3D12f9775a580000 kernel config: https://syzkaller.appspot.com/x/.config?x=3D294595c42a927f5= 5 dashboard link: https://syzkaller.appspot.com/bug?extid=3D65459fd3b61877d71= 7a3 compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Deb= ian) 2.44 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=3D1429cd5258000= 0 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=3D162eff5a580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/8d1ce7fc684d/disk-= 8004279c.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/9d97f0127a44/vmlinux-= 8004279c.xz kernel image: https://storage.googleapis.com/syzbot-assets/f36219283bb9/bzI= mage-8004279c.xz IMPORTANT: if you fix the issue, please add the following tag to the commit= : Reported-by: syzbot+65459fd3b61877d717a3@syzkaller.appspotmail.com =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.0.17/6008 is trying to acquire lock: ffff88807982dab8 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: inode_lock_sha= red include/linux/fs.h:1043 [inline] ffff88807982dab8 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow+0x= 42/0x70 fs/namei.c:1932 but task is already holding lock: ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/par= ams.c:602 [inline] ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xec/0x300 = kernel/params.c:587 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (param_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:614 [inline] __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776 ieee80211_rate_control_ops_get net/mac80211/rate.c:223 [inline] rate_control_alloc net/mac80211/rate.c:269 [inline] ieee80211_init_rate_ctrl_alg+0x1df/0x3b0 net/mac80211/rate.c:1016 ieee80211_register_hw+0x2950/0x4140 net/mac80211/main.c:1544 mac80211_hwsim_new_radio+0x2847/0x57d0 drivers/net/wireless/virtual/= mac80211_hwsim.c:5810 init_mac80211_hwsim+0x6db/0x7f0 drivers/net/wireless/virtual/mac8021= 1_hwsim.c:7173 do_one_initcall+0x11d/0x760 init/main.c:1382 do_initcall_level init/main.c:1444 [inline] do_initcalls init/main.c:1460 [inline] do_basic_setup init/main.c:1479 [inline] kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692 kernel_init+0x1f/0x1e0 init/main.c:1582 ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (rtnl_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:614 [inline] __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776 cgrp_css_online+0xa1/0x1f0 net/core/netprio_cgroup.c:157 online_css+0xb2/0x350 kernel/cgroup/cgroup.c:5732 css_create kernel/cgroup/cgroup.c:5820 [inline] cgroup_apply_control_enable+0x8bd/0xbd0 kernel/cgroup/cgroup.c:3389 cgroup_mkdir+0x57f/0x1330 kernel/cgroup/cgroup.c:6021 kernfs_iop_mkdir+0x111/0x190 fs/kernfs/dir.c:1273 vfs_mkdir+0x361/0x850 fs/namei.c:5233 filename_mkdirat+0x48b/0x5e0 fs/namei.c:5266 __do_sys_mkdirat fs/namei.c:5287 [inline] __se_sys_mkdirat fs/namei.c:5284 [inline] __x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5284 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (cgroup_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:614 [inline] __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776 cgroup_lock include/linux/cgroup.h:394 [inline] cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1732 cgroup_rmdir+0x22/0x2e0 kernel/cgroup/cgroup.c:6226 kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1291 vfs_rmdir fs/namei.c:5338 [inline] vfs_rmdir+0x328/0x8a0 fs/namei.c:5311 filename_rmdir+0x31a/0x5c0 fs/namei.c:5393 __do_sys_rmdir fs/namei.c:5416 [inline] __se_sys_rmdir fs/namei.c:5413 [inline] __x64_sys_rmdir+0x46/0x70 fs/namei.c:5413 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&type->i_mutex_dir_key#6){++++}-{4:4}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237 lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825 down_read+0x99/0x460 kernel/locking/rwsem.c:1537 inode_lock_shared include/linux/fs.h:1043 [inline] lookup_slow+0x42/0x70 fs/namei.c:1932 walk_component fs/namei.c:2279 [inline] lookup_last fs/namei.c:2780 [inline] path_lookupat+0x5e8/0xc40 fs/namei.c:2804 filename_lookup+0x202/0x590 fs/namei.c:2833 kern_path+0x37/0x50 fs/namei.c:3040 lookup_bdev+0xd8/0x280 block/bdev.c:1221 bdev_file_open_by_path+0x82/0x330 block/bdev.c:1094 add_device drivers/mtd/devices/block2mtd.c:279 [inline] block2mtd_setup2.isra.0+0x2ee/0xc70 drivers/mtd/devices/block2mtd.c:= 459 block2mtd_setup+0xbd/0xd0 drivers/mtd/devices/block2mtd.c:476 param_attr_store+0x199/0x300 kernel/params.c:589 module_attr_store+0x58/0x80 kernel/params.c:913 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6ac/0x1070 fs/read_write.c:688 ksys_write+0x12a/0x250 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &type->i_mutex_dir_key#6 --> rtnl_mutex --> param_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(param_lock); lock(rtnl_mutex); lock(param_lock); rlock(&type->i_mutex_dir_key#6); *** DEADLOCK *** 4 locks held by syz.0.17/6008: #0: ffff888037100420 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x25= 0 fs/read_write.c:740 #1: ffff888063a41488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0= x2c2/0x5f0 fs/kernfs/file.c:343 #2: ffff88803515ee18 (kn->active#4){.+.+}-{0:0}, at: kernfs_get_active_of = fs/kernfs/file.c:80 [inline] #2: ffff88803515ee18 (kn->active#4){.+.+}-{0:0}, at: kernfs_fop_write_iter= +0x332/0x5f0 fs/kernfs/file.c:344 #3: ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kerne= l/params.c:602 [inline] #3: ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xec/0= x300 kernel/params.c:587 stack backtrace: CPU: 1 UID: 0 PID: 6008 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(ful= l)=20 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Goo= gle 02/27/2026 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237 lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825 down_read+0x99/0x460 kernel/locking/rwsem.c:1537 inode_lock_shared include/linux/fs.h:1043 [inline] lookup_slow+0x42/0x70 fs/namei.c:1932 walk_component fs/namei.c:2279 [inline] lookup_last fs/namei.c:2780 [inline] path_lookupat+0x5e8/0xc40 fs/namei.c:2804 filename_lookup+0x202/0x590 fs/namei.c:2833 kern_path+0x37/0x50 fs/namei.c:3040 lookup_bdev+0xd8/0x280 block/bdev.c:1221 bdev_file_open_by_path+0x82/0x330 block/bdev.c:1094 add_device drivers/mtd/devices/block2mtd.c:279 [inline] block2mtd_setup2.isra.0+0x2ee/0xc70 drivers/mtd/devices/block2mtd.c:459 block2mtd_setup+0xbd/0xd0 drivers/mtd/devices/block2mtd.c:476 param_attr_store+0x199/0x300 kernel/params.c:589 module_attr_store+0x58/0x80 kernel/params.c:913 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x6ac/0x1070 fs/read_write.c:688 ksys_write+0x12a/0x250 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7faeae79c799 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 f= f 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffd3b6d7408 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007faeaea15fa0 RCX: 00007faeae79c799 RDX: 0000000000000025 RSI: 0000200000000000 RDI: 0000000000000004 RBP: 00007faeae832c99 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007faeaea15fac R14: 00007faeaea15fa0 R15: 00007faeaea15fa0 block2mtd: error: cannot open device =EF=BF=BDinX=EF=BF=BD=EF=BF=BD=EF=BF= =BD=EF=BF=BD=EF=BF=BD=14=C2=B1=EF=BF=BD=EF=BF=BDjFB=EF=BF=BD=1EB>U=EF=BF=BD= ;=DF=B8=0F=EF=BF=BDIlk=EF=BF=BD --- 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.