* Re: [syzbot] [kernfs?] possible deadlock in lookup_slow (3)
[not found] <000000000000dd477c0600d6d815@google.com>
@ 2026-03-13 3:08 ` syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-03-13 3:08 UTC (permalink / raw)
To: driver-core, gregkh, linux-fsdevel, linux-kernel, syzkaller-bugs,
tj
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=12f9775a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=294595c42a927f55
dashboard link: https://syzkaller.appspot.com/bug?extid=65459fd3b61877d717a3
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1429cd52580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=162eff5a580000
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/bzImage-8004279c.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+65459fd3b61877d717a3@syzkaller.appspotmail.com
======================================================
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_shared include/linux/fs.h:1043 [inline]
ffff88807982dab8 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow+0x42/0x70 fs/namei.c:1932
but task is already holding lock:
ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/params.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/mac80211_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/0x250 fs/read_write.c:740
#1: ffff888063a41488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 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 kernel/params.c:602 [inline]
#3: ffffffff8e69df08 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xec/0x300 kernel/params.c:587
stack backtrace:
CPU: 1 UID: 0 PID: 6008 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026
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+0x178/0x1c7 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 ff 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
</TASK>
block2mtd: error: cannot open device �inX�����\x14±��jFB�\x1eB>U�;߸\x0f�Ilk�
---
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.
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