======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G     U    I        
------------------------------------------------------
syz.1.3919/26456 is trying to acquire lock:
ffff888140460a20 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424

but task is already holding lock:
ffff888140460988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_drain+0x29c/0x570 fs/kernfs/dir.c:527

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #8 (&root->kernfs_rwsem){++++}-{4:4}:
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1537
       kernfs_find_and_get_ns+0x2f/0x70 fs/kernfs/dir.c:933
       kernfs_find_and_get include/linux/kernfs.h:612 [inline]
       sysfs_remove_group+0x73/0x180 fs/sysfs/group.c:311
       topology_remove_dev+0x22/0x30 drivers/base/topology.c:199
       cpuhp_invoke_callback+0x3d2/0xa10 kernel/cpu.c:195
       __cpuhp_invoke_callback_range+0x101/0x210 kernel/cpu.c:968
       cpuhp_invoke_callback_range kernel/cpu.c:992 [inline]
       cpuhp_down_callbacks kernel/cpu.c:1382 [inline]
       _cpu_down+0x422/0xf20 kernel/cpu.c:1443
       __cpu_down_maps_locked+0x6c/0x90 kernel/cpu.c:1468
       work_for_cpu_fn+0x52/0xa0 kernel/workqueue.c:6774
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3263
       process_scheduled_works kernel/workqueue.c:3346 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x56a/0x730 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #7 (cpu_hotplug_lock){++++}-{0:0}:
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       cpus_read_lock+0x42/0x160 kernel/cpu.c:491
       static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
       udp_encap_enable net/ipv4/udp.c:820 [inline]
       udp_tunnel_encap_enable include/net/udp_tunnel.h:203 [inline]
       udp_tunnel_encap_enable include/net/udp_tunnel.h:194 [inline]
       udp_lib_setsockopt+0x3f3/0xcf0 net/ipv4/udp.c:3057
       udp_setsockopt+0xbc/0xd0 net/ipv4/udp.c:3107
       do_sock_setsockopt+0xf3/0x1d0 net/socket.c:2360
       __sys_setsockopt+0x120/0x1a0 net/socket.c:2385
       __do_sys_setsockopt net/socket.c:2391 [inline]
       __se_sys_setsockopt net/socket.c:2388 [inline]
       __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2388
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
       lock_sock include/net/sock.h:1679 [inline]
       inet_shutdown+0x67/0x440 net/ipv4/af_inet.c:907
       nbd_mark_nsock_dead+0xae/0x5d0 drivers/block/nbd.c:318
       recv_work+0x671/0xa80 drivers/block/nbd.c:1018
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3263
       process_scheduled_works kernel/workqueue.c:3346 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x56a/0x730 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
       nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1204
       blk_mq_dispatch_rq_list+0x413/0x1e20 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
       blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
       submit_bio_noacct+0xbbb/0x1f60 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4024
       read_mapping_folio include/linux/pagemap.h:999 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:694
       do_dentry_open+0x97f/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1097
       do_open fs/namei.c:3975 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1196
       blk_mq_dispatch_rq_list+0x413/0x1e20 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
       blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
       submit_bio_noacct+0xbbb/0x1f60 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4024
       read_mapping_folio include/linux/pagemap.h:999 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:694
       do_dentry_open+0x97f/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1097
       do_open fs/namei.c:3975 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:173 [inline]
       __synchronize_srcu+0xa1/0x290 kernel/rcu/srcutree.c:1439
       blk_mq_wait_quiesce_done block/blk-mq.c:283 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:280 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:303 [inline]
       blk_mq_quiesce_queue+0x149/0x1b0 block/blk-mq.c:298
       queue_wb_lat_store+0x269/0x3d0 block/blk-sysfs.c:684
       queue_attr_store+0x268/0x310 block/blk-sysfs.c:869
       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/0x4b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#69){++++}-{0:0}:
       blk_alloc_queue+0x619/0x760 block/blk-core.c:461
       blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4399
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4446
       add_mtd_blktrans_dev+0x7ad/0x15a0 drivers/mtd/mtd_blkdevs.c:343
       mtdblock_add_mtd+0x1cc/0x270 drivers/mtd/mtdblock.c:333
       blktrans_notify_add drivers/mtd/mtd_blkdevs.c:464 [inline]
       blktrans_notify_add+0xa2/0xf0 drivers/mtd/mtd_blkdevs.c:456
       add_mtd_device+0xb84/0x1850 drivers/mtd/mtdcore.c:820
       mtd_device_parse_register+0x7c2/0xb10 drivers/mtd/mtdcore.c:1133
       mtdram_init_device+0x298/0x350 drivers/mtd/devices/mtdram.c:146
       init_mtdram+0xba/0x1b0 drivers/mtd/devices/mtdram.c:171
       do_one_initcall+0x120/0x6e0 init/main.c:1283
       do_initcall_level init/main.c:1345 [inline]
       do_initcalls init/main.c:1361 [inline]
       do_basic_setup init/main.c:1380 [inline]
       kernel_init_freeable+0x5c2/0x910 init/main.c:1593
       kernel_init+0x1c/0x2b0 init/main.c:1483
       ret_from_fork+0x56a/0x730 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4269 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4283
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4897 [inline]
       slab_alloc_node mm/slub.c:5221 [inline]
       kmem_cache_alloc_noprof+0x5b/0x6e0 mm/slub.c:5252
       __kernfs_iattrs+0x124/0x3e0 fs/kernfs/inode.c:36
       kernfs_iattrs fs/kernfs/inode.c:61 [inline]
       __kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:74
       kernfs_iop_setattr+0xda/0x120 fs/kernfs/inode.c:128
       notify_change+0x6a9/0x1230 fs/attr.c:552
       do_truncate+0x1d7/0x230 fs/open.c:68
       handle_truncate fs/namei.c:3596 [inline]
       do_open fs/namei.c:3979 [inline]
       path_openat+0x2678/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       down_write+0x92/0x200 kernel/locking/rwsem.c:1590
       kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424
       __kernfs_remove+0x2c0/0x8a0 fs/kernfs/dir.c:1514
       kernfs_remove_by_name_ns+0x68/0x110 fs/kernfs/dir.c:1717
       kernfs_remove_by_name include/linux/kernfs.h:633 [inline]
       cgroup_rm_file kernel/cgroup/cgroup.c:1761 [inline]
       cgroup_addrm_files+0x82c/0xc20 kernel/cgroup/cgroup.c:4484
       css_clear_dir+0x1da/0x290 kernel/cgroup/cgroup.c:1780
       cgroup_destroy_locked+0x3a4/0x710 kernel/cgroup/cgroup.c:6193
       cgroup_rmdir+0x35/0x2b0 kernel/cgroup/cgroup.c:6233
       kernfs_iop_rmdir+0x103/0x170 fs/kernfs/dir.c:1286
       vfs_rmdir fs/namei.c:4548 [inline]
       vfs_rmdir+0x206/0x690 fs/namei.c:4525
       do_rmdir+0x2e8/0x3c0 fs/namei.c:4603
       __do_sys_rmdir fs/namei.c:4622 [inline]
       __se_sys_rmdir fs/namei.c:4620 [inline]
       __x64_sys_rmdir+0xc5/0x110 fs/namei.c:4620
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4b0 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:
  &root->kernfs_iattr_rwsem --> cpu_hotplug_lock --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&root->kernfs_rwsem);
                               lock(cpu_hotplug_lock);
                               lock(&root->kernfs_rwsem);
  lock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

5 locks held by syz.1.3919/26456:
 #0: ffff8880338de420 (sb_writers#9){.+.+}-{0:0}, at: do_rmdir+0x1e2/0x3c0 fs/namei.c:4591
 #1: ffff88805fa91a20 (&type->i_mutex_dir_key#6/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1024 [inline]
 #1: ffff88805fa91a20 (&type->i_mutex_dir_key#6/1){+.+.}-{4:4}, at: do_rmdir+0x233/0x3c0 fs/namei.c:4595
 #2: ffff8880533a9f18 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: inode_lock include/linux/fs.h:979 [inline]
 #2: ffff8880533a9f18 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: vfs_rmdir fs/namei.c:4537 [inline]
 #2: ffff8880533a9f18 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: vfs_rmdir+0xe9/0x690 fs/namei.c:4525
 #3: ffffffff8e21cd48 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_lock include/linux/cgroup.h:393 [inline]
 #3: ffffffff8e21cd48 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_kn_lock_live+0x116/0x520 kernel/cgroup/cgroup.c:1735
 #4: ffff888140460988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_drain+0x29c/0x570 fs/kernfs/dir.c:527

stack backtrace:
CPU: 1 UID: 0 PID: 26456 Comm: syz.1.3919 Tainted: G     U    I         syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [I]=FIRMWARE_WORKAROUND
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 down_write+0x92/0x200 kernel/locking/rwsem.c:1590
 kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424
 __kernfs_remove+0x2c0/0x8a0 fs/kernfs/dir.c:1514
 kernfs_remove_by_name_ns+0x68/0x110 fs/kernfs/dir.c:1717
 kernfs_remove_by_name include/linux/kernfs.h:633 [inline]
 cgroup_rm_file kernel/cgroup/cgroup.c:1761 [inline]
 cgroup_addrm_files+0x82c/0xc20 kernel/cgroup/cgroup.c:4484
 css_clear_dir+0x1da/0x290 kernel/cgroup/cgroup.c:1780
 cgroup_destroy_locked+0x3a4/0x710 kernel/cgroup/cgroup.c:6193
 cgroup_rmdir+0x35/0x2b0 kernel/cgroup/cgroup.c:6233
 kernfs_iop_rmdir+0x103/0x170 fs/kernfs/dir.c:1286
 vfs_rmdir fs/namei.c:4548 [inline]
 vfs_rmdir+0x206/0x690 fs/namei.c:4525
 do_rmdir+0x2e8/0x3c0 fs/namei.c:4603
 __do_sys_rmdir fs/namei.c:4622 [inline]
 __se_sys_rmdir fs/namei.c:4620 [inline]
 __x64_sys_rmdir+0xc5/0x110 fs/namei.c:4620
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2d0cf8eec9
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:00007f2d0deda038 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00007f2d0d1e6090 RCX: 00007f2d0cf8eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000300
RBP: 00007f2d0d011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2d0d1e6128 R14: 00007f2d0d1e6090 R15: 00007ffd264479a8
 </TASK>