syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G     U  W    L XTNJ
------------------------------------------------------
syz.2.9284/30175 is trying to acquire lock:
ffff88805a5bd0c8 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1042 [inline]
ffff88805a5bd0c8 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow+0x42/0x70 fs/namei.c:1882

but task is already holding lock:
ffffffff8e286c08 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/params.c:608 [inline]
ffffffff8e286c08 (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+0x1aa/0x1ca0 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+0x18d/0x680 net/mac80211/rate.c:1016
       ieee80211_register_hw+0x21b5/0x4160 net/mac80211/main.c:1534
       mac80211_hwsim_new_radio+0x3323/0x5150 drivers/net/wireless/virtual/mac80211_hwsim.c:5810
       init_mac80211_hwsim+0x44e/0x920 drivers/net/wireless/virtual/mac80211_hwsim.c:7175
       do_one_initcall+0x123/0x680 init/main.c:1378
       do_initcall_level init/main.c:1440 [inline]
       do_initcalls init/main.c:1456 [inline]
       do_basic_setup init/main.c:1475 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1688
       kernel_init+0x1c/0x2b0 init/main.c:1578
       ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #2 (rtnl_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       cgrp_css_online+0xa2/0x1f0 net/core/netprio_cgroup.c:157
       online_css+0xb2/0x350 kernel/cgroup/cgroup.c:5731
       css_create kernel/cgroup/cgroup.c:5819 [inline]
       cgroup_apply_control_enable+0x702/0xbb0 kernel/cgroup/cgroup.c:3388
       cgroup_mkdir+0x5d9/0x12d0 kernel/cgroup/cgroup.c:6020
       kernfs_iop_mkdir+0x111/0x190 fs/kernfs/dir.c:1273
       vfs_mkdir+0x731/0xb60 fs/namei.c:5139
       do_mkdirat+0x442/0x5e0 fs/namei.c:5173
       __do_sys_mkdirat fs/namei.c:5195 [inline]
       __se_sys_mkdirat fs/namei.c:5193 [inline]
       __x64_sys_mkdirat+0x83/0xb0 fs/namei.c:5193
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/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+0x1aa/0x1ca0 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+0x20/0x290 kernel/cgroup/cgroup.c:6225
       kernfs_iop_rmdir+0x106/0x170 fs/kernfs/dir.c:1291
       vfs_rmdir fs/namei.c:5245 [inline]
       vfs_rmdir+0x382/0x840 fs/namei.c:5218
       do_rmdir+0x3be/0x560 fs/namei.c:5300
       __do_sys_rmdir fs/namei.c:5324 [inline]
       __se_sys_rmdir fs/namei.c:5322 [inline]
       __x64_sys_rmdir+0xc5/0x110 fs/namei.c:5322
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/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+0x1669/0x2890 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
       down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:1042 [inline]
       lookup_slow+0x42/0x70 fs/namei.c:1882
       walk_component fs/namei.c:2229 [inline]
       lookup_last fs/namei.c:2730 [inline]
       path_lookupat+0x5e9/0xc40 fs/namei.c:2754
       filename_lookup+0x224/0x5f0 fs/namei.c:2783
       kern_path+0x35/0x50 fs/namei.c:2996
       lookup_bdev+0xd8/0x280 block/bdev.c:1222
       bdev_file_open_by_path+0x82/0x330 block/bdev.c:1095
       add_device drivers/mtd/devices/block2mtd.c:279 [inline]
       block2mtd_setup2+0x317/0xe10 drivers/mtd/devices/block2mtd.c:459
       block2mtd_setup+0xbd/0x110 drivers/mtd/devices/block2mtd.c:476
       param_attr_store+0x199/0x300 kernel/params.c:589
       module_attr_store+0x58/0x80 kernel/params.c:919
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x7d3/0x11d0 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/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 ***

5 locks held by syz.2.9284/30175:
 #0: ffff888024e65978 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1255
 #1: ffff88803496a420 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:738
 #2: ffff888031955088 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343
 #3: ffff888032d172d8 (kn->active#4){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline]
 #3: ffff888032d172d8 (kn->active#4){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2ff/0x570 fs/kernfs/file.c:344
 #4: ffffffff8e286c08 (param_lock){+.+.}-{4:4}, at: kernel_param_lock kernel/params.c:608 [inline]
 #4: ffffffff8e286c08 (param_lock){+.+.}-{4:4}, at: param_attr_store+0xec/0x300 kernel/params.c:587

stack backtrace:
CPU: 0 UID: 0 PID: 30175 Comm: syz.2.9284 Tainted: G     U  W    L XTNJ syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [W]=WARN, [L]=SOFTLOCKUP, [X]=AUX, [T]=RANDSTRUCT, [N]=TEST, [J]=FWCTL
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x340 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+0x1669/0x2890 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
 down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
 inode_lock_shared include/linux/fs.h:1042 [inline]
 lookup_slow+0x42/0x70 fs/namei.c:1882
 walk_component fs/namei.c:2229 [inline]
 lookup_last fs/namei.c:2730 [inline]
 path_lookupat+0x5e9/0xc40 fs/namei.c:2754
 filename_lookup+0x224/0x5f0 fs/namei.c:2783
 kern_path+0x35/0x50 fs/namei.c:2996
 lookup_bdev+0xd8/0x280 block/bdev.c:1222
 bdev_file_open_by_path+0x82/0x330 block/bdev.c:1095
 add_device drivers/mtd/devices/block2mtd.c:279 [inline]
 block2mtd_setup2+0x317/0xe10 drivers/mtd/devices/block2mtd.c:459
 block2mtd_setup+0xbd/0x110 drivers/mtd/devices/block2mtd.c:476
 param_attr_store+0x199/0x300 kernel/params.c:589
 module_attr_store+0x58/0x80 kernel/params.c:919
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d3/0x11d0 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa906f8f7c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa907f06038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fa9071e5fa0 RCX: 00007fa906f8f7c9
RDX: 0000000000000024 RSI: 0000200000000140 RDI: 0000000000000006
RBP: 00007fa907013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa9071e6038 R14: 00007fa9071e5fa0 R15: 00007ffc70b983d8
 </TASK>
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