* [syzbot] [cgroups?] possible deadlock in cgroup_kn_lock_live (2)
@ 2026-04-10 17:24 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-04-10 17:24 UTC (permalink / raw)
To: cgroups, hannes, linux-kernel, mkoutny, syzkaller-bugs, tj
Hello,
syzbot found the following issue on:
HEAD commit: 591cd656a1bf Linux 7.0-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=138ddd02580000
kernel config: https://syzkaller.appspot.com/x/.config?x=64e78d99d9bf8b4c
dashboard link: https://syzkaller.appspot.com/bug?extid=6dc923fb5b4671f0fcf0
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bf0f027c93ec/disk-591cd656.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/60d829be17f4/vmlinux-591cd656.xz
kernel image: https://storage.googleapis.com/syzbot-assets/673c009c7550/bzImage-591cd656.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6dc923fb5b4671f0fcf0@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.1.1390/12323 is trying to acquire lock:
ffffffff8e84a7c8 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_lock include/linux/cgroup.h:394 [inline]
ffffffff8e84a7c8 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1732
but task is already holding lock:
ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: inode_lock include/linux/fs.h:1028 [inline]
ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir fs/namei.c:5329 [inline]
ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir+0xed/0x8a0 fs/namei.c:5317
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (&type->i_mutex_dir_key#7){++++}-{4:4}:
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:2786 [inline]
path_lookupat+0x5e8/0xc40 fs/namei.c:2810
filename_lookup+0x202/0x590 fs/namei.c:2839
kern_path+0x37/0x50 fs/namei.c:3046
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
-> #2 (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:5809
init_mac80211_hwsim+0x6db/0x7f0 drivers/net/wireless/virtual/mac80211_hwsim.c:7172
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
-> #1 (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:5739
css_create kernel/cgroup/cgroup.c:5827 [inline]
cgroup_apply_control_enable+0x8bd/0xbd0 kernel/cgroup/cgroup.c:3390
cgroup_mkdir+0x57f/0x1330 kernel/cgroup/cgroup.c:6028
kernfs_iop_mkdir+0x111/0x190 fs/kernfs/dir.c:1273
vfs_mkdir+0x361/0x850 fs/namei.c:5239
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5272
__do_sys_mkdirat fs/namei.c:5293 [inline]
__se_sys_mkdirat fs/namei.c:5290 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5290
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 (cgroup_mutex){+.+.}-{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
__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+0x22/0x300 kernel/cgroup/cgroup.c:6305
kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1291
vfs_rmdir fs/namei.c:5344 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5317
filename_rmdir+0x31a/0x5c0 fs/namei.c:5399
__do_sys_rmdir fs/namei.c:5422 [inline]
__se_sys_rmdir fs/namei.c:5419 [inline]
__x64_sys_rmdir+0x46/0x70 fs/namei.c:5419
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:
cgroup_mutex --> param_lock --> &type->i_mutex_dir_key#7
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&type->i_mutex_dir_key#7);
lock(param_lock);
lock(&type->i_mutex_dir_key#7);
lock(cgroup_mutex);
*** DEADLOCK ***
3 locks held by syz.1.1390/12323:
#0: ffff88807fec2420 (sb_writers#10){.+.+}-{0:0}, at: filename_rmdir+0x1ff/0x5c0 fs/namei.c:5388
#1: ffff88805cae8148 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1073 [inline]
#1: ffff88805cae8148 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2929 [inline]
#1: ffff88805cae8148 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2940 [inline]
#1: ffff88805cae8148 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: filename_rmdir+0x258/0x5c0 fs/namei.c:5392
#2: ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: inode_lock include/linux/fs.h:1028 [inline]
#2: ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir fs/namei.c:5329 [inline]
#2: ffff888059c1d5c0 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir+0xed/0x8a0 fs/namei.c:5317
stack backtrace:
CPU: 0 UID: 0 PID: 12323 Comm: syz.1.1390 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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
__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+0x22/0x300 kernel/cgroup/cgroup.c:6305
kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1291
vfs_rmdir fs/namei.c:5344 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5317
filename_rmdir+0x31a/0x5c0 fs/namei.c:5399
__do_sys_rmdir fs/namei.c:5422 [inline]
__se_sys_rmdir fs/namei.c:5419 [inline]
__x64_sys_rmdir+0x46/0x70 fs/namei.c:5419
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: 0033:0x7f8142b9c819
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:00007f81439b7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00007f8142e16180 RCX: 00007f8142b9c819
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000040
RBP: 00007f8142c32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8142e16218 R14: 00007f8142e16180 R15: 00007ffc92158f68
</TASK>
---
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2026-04-10 17:24 [syzbot] [cgroups?] possible deadlock in cgroup_kn_lock_live (2) syzbot
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