From: syzbot <syzbot+6dc923fb5b4671f0fcf0@syzkaller.appspotmail.com>
To: amir73il@gmail.com, cgroups@vger.kernel.org, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org,
miklos@szeredi.hu, mkoutny@suse.com,
syzkaller-bugs@googlegroups.com, tj@kernel.org
Subject: Re: [syzbot] [cgroups?] [overlayfs?] possible deadlock in cgroup_kn_lock_live (2)
Date: Thu, 15 Oct 2026 18:51:29 -0700 [thread overview]
Message-ID: <6ad18321.7952420f.283480.0192.GAE@google.com> (raw)
In-Reply-To: <69d93248.050a0220.3030df.002f.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: 045958acaa75 Merge tag 'net-7.3-rc8' of git://git.kernel.o..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1067ffd1580000
kernel config: https://syzkaller.appspot.com/x/.config?x=44ac479246d4559b
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
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1467ffd1580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6dc923fb5b4671f0fcf0@syzkaller.appspotmail.com
block2mtd: error: cannot open device /tmp/cg/nonexistent_mtd_bdev
block2mtd: error: cannot open device /dev/nonexistent_mtd_bdev
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor140/5993 is trying to acquire lock:
ffffffff8fe523e0 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_lock include/linux/cgroup.h:482 [inline]
ffffffff8fe523e0 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1719
but task is already holding lock:
ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir fs/namei.c:5529 [inline]
ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir+0xed/0x8a0 fs/namei.c:5517
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}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
down_read+0x99/0x4c0 kernel/locking/rwsem.c:1574
inode_lock_shared include/linux/fs.h:1039 [inline]
lookup_slow+0x42/0x70 fs/namei.c:1935
walk_component fs/namei.c:2311 [inline]
lookup_last fs/namei.c:2818 [inline]
path_lookupat+0x5e8/0xc40 fs/namei.c:2842
filename_lookup+0x202/0x590 fs/namei.c:2871
kern_path+0x37/0x50 fs/namei.c:3065
lookup_bdev+0xd8/0x2a0 block/bdev.c:1268
bdev_file_open_by_path+0x82/0x330 block/bdev.c:1123
add_device drivers/mtd/devices/block2mtd.c:279 [inline]
block2mtd_setup2.isra.0+0x2f8/0xc60 drivers/mtd/devices/block2mtd.c:459
block2mtd_setup+0xbd/0xd0 drivers/mtd/devices/block2mtd.c:476
param_attr_store+0x199/0x300 kernel/params.c:591
module_attr_store+0x58/0x80 kernel/params.c:906
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_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x121/0x770 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (param_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
ieee80211_rate_control_ops_get net/mac80211/rate.c:221 [inline]
rate_control_alloc net/mac80211/rate.c:267 [inline]
ieee80211_init_rate_ctrl_alg+0x1df/0x3b0 net/mac80211/rate.c:1016
ieee80211_register_hw+0x2c5b/0x45c0 net/mac80211/main.c:1565
mac80211_hwsim_new_radio+0x2b08/0x6510 drivers/net/wireless/virtual/mac80211_hwsim_main.c:6143
init_mac80211_hwsim+0x5e2/0x6f0 drivers/net/wireless/virtual/mac80211_hwsim_main.c:7633
do_one_initcall+0x11c/0x6f0 init/main.c:1362
do_initcall_level init/main.c:1424 [inline]
do_initcalls init/main.c:1440 [inline]
do_basic_setup init/main.c:1460 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1675
kernel_init+0x21/0x1e0 init/main.c:1565
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (rtnl_mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
cgrp_css_online+0xa1/0x1f0 net/core/netprio_cgroup.c:157
online_css+0xb2/0x350 kernel/cgroup/cgroup.c:5871
css_create kernel/cgroup/cgroup.c:5949 [inline]
cgroup_apply_control_enable+0xa8d/0xdd0 kernel/cgroup/cgroup.c:3460
cgroup_mkdir+0x57f/0x1330 kernel/cgroup/cgroup.c:6150
kernfs_iop_mkdir+0x111/0x190 fs/kernfs/dir.c:1305
vfs_mkdir+0x364/0x850 fs/namei.c:5439
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5472
__do_sys_mkdirat fs/namei.c:5493 [inline]
__se_sys_mkdirat fs/namei.c:5490 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5490
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x121/0x770 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (cgroup_mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
cgroup_lock include/linux/cgroup.h:482 [inline]
cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1719
cgroup_rmdir+0x22/0x2f0 kernel/cgroup/cgroup.c:6402
kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1323
vfs_rmdir fs/namei.c:5544 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5517
filename_rmdir+0x31a/0x5c0 fs/namei.c:5601
__do_sys_rmdir fs/namei.c:5624 [inline]
__se_sys_rmdir fs/namei.c:5621 [inline]
__x64_sys_rmdir+0x46/0x70 fs/namei.c:5621
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x121/0x770 arch/x86/entry/syscall_64.c:84
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 ***
locks held by syz-executor140/5993: 3, last CPU#0:
#0: ffff88807ea22460 (sb_writers#10){.+.+}-{0:0}, at: filename_rmdir+0x1ff/0x5c0 fs/namei.c:5590
#1: ffff888076d68f80 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1069 [inline]
#1: ffff888076d68f80 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2947 [inline]
#1: ffff888076d68f80 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2971 [inline]
#1: ffff888076d68f80 (&type->i_mutex_dir_key#7/1){+.+.}-{4:4}, at: filename_rmdir+0x258/0x5c0 fs/namei.c:5594
#2: ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
#2: ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir fs/namei.c:5529 [inline]
#2: ffff888071de6740 (&type->i_mutex_dir_key#7){++++}-{4:4}, at: vfs_rmdir+0xed/0x8a0 fs/namei.c:5517
stack backtrace:
CPU: 0 UID: 0 PID: 5993 Comm: syz-executor140 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
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+0x178/0x1be kernel/locking/lockdep.c:2087
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
cgroup_lock include/linux/cgroup.h:482 [inline]
cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1719
cgroup_rmdir+0x22/0x2f0 kernel/cgroup/cgroup.c:6402
kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1323
vfs_rmdir fs/namei.c:5544 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5517
filename_rmdir+0x31a/0x5c0 fs/namei.c:5601
__do_sys_rmdir fs/namei.c:5624 [inline]
__se_sys_rmdir fs/namei.c:5621 [inline]
__x64_sys_rmdir+0x46/0x70 fs/namei.c:5621
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x121/0x770 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f81c4d28557
Code: 00 00 90 48 83 ec 10 48 63 ff 45 31 c9 45 31 c0 6a 00 31 c9 e8 4a 02 02 00 48 83 c4 18 c3 0f 1f 44 00 00 b8 54 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffe71e77668 EFLAGS: 00000206 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f81c4d28557
RDX: 0000000000000000 RSI: 00007f81c4db03a3 RDI: 00007f81c4d83e7b
RBP: 00007ffe71e77670 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 00007f81c4d83e50
R13: 00007f81c4d83e7b R14: 000000000000001e R15: 0000000000000002
</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.
prev parent reply other threads:[~2026-10-16 1:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-10 17:24 [syzbot] [cgroups?] possible deadlock in cgroup_kn_lock_live (2) syzbot
2026-10-16 1:51 ` syzbot [this message]
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