======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.1.219/6958 is trying to acquire lock:
ffff88802792bbc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681

but task is already holding lock:
ffff888057deb0b8 (&eq->sysfs_lock){+.+.}-{4:4}, at: elevator_exit+0x88/0xf0 block/elevator.c:160

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&eq->sysfs_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       elevator_exit+0x88/0xf0 block/elevator.c:160
       elevator_switch+0x3a7/0x7e0 block/elevator.c:580
       elevator_change+0x352/0x530 block/elevator.c:681
       elevator_set_none+0x92/0xf0 block/elevator.c:769
       blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
       __del_gendisk+0x2e3/0xb20 block/genhd.c:739
       del_gendisk+0x10e/0x1b0 block/genhd.c:819
       loop_remove drivers/block/loop.c:2112 [inline]
       loop_control_remove drivers/block/loop.c:2171 [inline]
       loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       elevator_change+0x1bc/0x530 block/elevator.c:679
       elv_iosched_store+0x3be/0x460 block/elevator.c:826
       queue_attr_store+0x25f/0x2f0 block/blk-sysfs.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+0x6ac/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#17){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       blk_alloc_queue+0x610/0x790 block/blk-core.c:504
       blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
       loop_add+0x498/0xb60 drivers/block/loop.c:2041
       loop_init+0x1d3/0x200 drivers/block/loop.c:2280
       do_one_initcall+0x11d/0x700 init/main.c:1347
       do_initcall_level init/main.c:1409 [inline]
       do_initcalls init/main.c:1425 [inline]
       do_basic_setup init/main.c:1445 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658
       kernel_init+0x1f/0x1e0 init/main.c:1548
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __fs_reclaim_acquire mm/page_alloc.c:4329 [inline]
       fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4343
       might_alloc include/linux/sched/mm.h:317 [inline]
       prepare_alloc_pages+0x166/0x5f0 mm/page_alloc.c:5048
       __alloc_frozen_pages_noprof+0x1af/0x2dc0 mm/page_alloc.c:5293
       __alloc_pages_noprof+0xb/0x110 mm/page_alloc.c:5338
       __alloc_pages_node_noprof include/linux/gfp.h:291 [inline]
       alloc_pages_node_noprof include/linux/gfp.h:318 [inline]
       pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
       pcpu_populate_chunk+0x118/0x990 mm/percpu-vm.c:285
       pcpu_alloc_noprof+0x881/0x1ca0 mm/percpu.c:1876
       xt_percpu_counter_alloc+0x13e/0x1b0 net/netfilter/x_tables.c:2137
       find_check_entry.isra.0+0xc2/0xa00 net/ipv6/netfilter/ip6_tables.c:545
       translate_table+0xc31/0x16c0 net/ipv6/netfilter/ip6_tables.c:733
       ip6t_register_table+0x106/0x2c0 net/ipv6/netfilter/ip6_tables.c:1749
       ip6table_security_table_init+0x40/0x60 net/ipv6/netfilter/ip6table_security.c:45
       xt_find_table_lock+0x2db/0x520 net/netfilter/x_tables.c:1353
       xt_request_find_table_lock+0x28/0xf0 net/netfilter/x_tables.c:1378
       get_info+0x1a7/0x770 net/ipv6/netfilter/ip6_tables.c:977
       do_ip6t_get_ctl+0x231/0xc30 net/ipv6/netfilter/ip6_tables.c:1669
       nf_getsockopt+0x7c/0xe0 net/netfilter/nf_sockopt.c:116
       ipv6_getsockopt+0x207/0x2a0 net/ipv6/ipv6_sockglue.c:1464
       tcp_getsockopt+0xa1/0x110 net/ipv4/tcp.c:4864
       do_sock_getsockopt+0x50a/0x6e0 net/socket.c:2474
       __sys_getsockopt+0x148/0x260 net/socket.c:2505
       __do_sys_getsockopt net/socket.c:2512 [inline]
       __se_sys_getsockopt net/socket.c:2509 [inline]
       __x64_sys_getsockopt+0xbd/0x160 net/socket.c:2509
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (pcpu_alloc_mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       pcpu_alloc_noprof+0xe87/0x1ca0 mm/percpu.c:1788
       percpu_ref_init+0x37/0x3f0 lib/percpu-refcount.c:72
       blkg_alloc+0xf0/0xf80 block/blk-cgroup.c:313
       blkg_conf_prep+0x46e/0xf10 block/blk-cgroup.c:873
       tg_set_conf.isra.0+0x1ed/0x500 block/blk-throttle.c:1373
       cgroup_file_write+0x1e6/0x8a0 kernel/cgroup/cgroup.c:4337
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6ac/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&q->blkcg_mutex){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681
       bfq_exit_queue+0x29d/0x430 block/bfq-iosched.c:7165
       blk_mq_exit_sched+0x20e/0x4e0 block/blk-mq-sched.c:702
       elevator_exit+0x93/0xf0 block/elevator.c:161
       elevator_switch+0x3a7/0x7e0 block/elevator.c:580
       elevator_change+0x352/0x530 block/elevator.c:681
       elevator_set_none+0x92/0xf0 block/elevator.c:769
       blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
       __del_gendisk+0x2e3/0xb20 block/genhd.c:739
       del_gendisk+0x10e/0x1b0 block/genhd.c:819
       loop_remove drivers/block/loop.c:2112 [inline]
       loop_control_remove drivers/block/loop.c:2171 [inline]
       loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 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:
  &q->blkcg_mutex --> &q->elevator_lock --> &eq->sysfs_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&eq->sysfs_lock);
                               lock(&q->elevator_lock);
                               lock(&eq->sysfs_lock);
  lock(&q->blkcg_mutex);

 *** DEADLOCK ***

3 locks held by syz.1.219/6958:
 #0: ffff8880278463a0 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x106/0x1b0 block/genhd.c:818
 #1: ffff88802792bd68 (&q->elevator_lock){+.+.}-{4:4}, at: elevator_change+0x1bc/0x530 block/elevator.c:679
 #2: ffff888057deb0b8 (&eq->sysfs_lock){+.+.}-{4:4}, at: elevator_exit+0x88/0xf0 block/elevator.c:160

stack backtrace:
CPU: 1 UID: 0 PID: 6958 Comm: syz.1.219 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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+0xeb/0xe60 kernel/locking/lockdep.c:3165
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681
 bfq_exit_queue+0x29d/0x430 block/bfq-iosched.c:7165
 blk_mq_exit_sched+0x20e/0x4e0 block/blk-mq-sched.c:702
 elevator_exit+0x93/0xf0 block/elevator.c:161
 elevator_switch+0x3a7/0x7e0 block/elevator.c:580
 elevator_change+0x352/0x530 block/elevator.c:681
 elevator_set_none+0x92/0xf0 block/elevator.c:769
 blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
 __del_gendisk+0x2e3/0xb20 block/genhd.c:739
 del_gendisk+0x10e/0x1b0 block/genhd.c:819
 loop_remove drivers/block/loop.c:2112 [inline]
 loop_control_remove drivers/block/loop.c:2171 [inline]
 loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f07b519e019
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:00007f07b60b9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f07b5426180 RCX: 00007f07b519e019
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 000000000000000a
RBP: 00007f07b523500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f07b5426218 R14: 00007f07b5426180 R15: 00007ffef5b69f28
 </TASK>