======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.8.1099/9684 is trying to acquire lock:
ffffffff8ef83160 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0xe87/0x1ca0 mm/percpu.c:1788

but task is already holding lock:
ffff8880279cbbc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xbc/0xf10 block/blk-cgroup.c:843

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&q->blkcg_mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bc0 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+0x1cf/0x7e0 block/elevator.c:580
       elevator_change+0x352/0x530 block/elevator.c:681
       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+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+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&eq->sysfs_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
       elevator_exit+0x88/0xf0 block/elevator.c:160
       elevator_switch+0x1cf/0x7e0 block/elevator.c:580
       elevator_change+0x352/0x530 block/elevator.c:681
       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+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+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bc0 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+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+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#66){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       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
       null_add_dev+0xdf8/0x1df0 drivers/block/null_blk/main.c:2008
       null_create_dev drivers/block/null_blk/main.c:2106 [inline]
       null_init+0x3a4/0x480 drivers/block/null_blk/main.c:2178
       do_one_initcall+0x11c/0x6f0 init/main.c:1353
       do_initcall_level init/main.c:1415 [inline]
       do_initcalls init/main.c:1431 [inline]
       do_basic_setup init/main.c:1451 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
       kernel_init+0x21/0x1e0 init/main.c:1556
       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 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       __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
       iommu_dma_init_fq_percpu drivers/iommu/dma-iommu.c:321 [inline]
       iommu_dma_init_fq+0x1da/0x7e0 drivers/iommu/dma-iommu.c:347
       iommu_dma_init_domain drivers/iommu/dma-iommu.c:720 [inline]
       iommu_setup_dma_ops+0x11df/0x1620 drivers/iommu/dma-iommu.c:2159
       bus_iommu_probe+0x264/0x550 drivers/iommu/iommu.c:1983
       iommu_device_register+0x1af/0x280 drivers/iommu/iommu.c:307
       intel_iommu_init+0x2020/0x2990 drivers/iommu/intel/iommu.c:2662
       pci_iommu_init+0x3c/0x80 arch/x86/kernel/pci-dma.c:174
       do_one_initcall+0x11c/0x6f0 init/main.c:1353
       do_initcall_level init/main.c:1415 [inline]
       do_initcalls init/main.c:1431 [inline]
       do_basic_setup init/main.c:1451 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
       kernel_init+0x21/0x1e0 init/main.c:1556
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (pcpu_alloc_mutex){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
       check_prevs_add kernel/locking/lockdep.c:3300 [inline]
       validate_chain kernel/locking/lockdep.c:3924 [inline]
       __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bc0 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+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+0x123/0x790 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:
  pcpu_alloc_mutex --> &eq->sysfs_lock --> &q->blkcg_mutex

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

locks held by syz.8.1099/9684: 6, last CPU#1:
 #0: ffff88803dc91eb0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259
 #1: ffff8880360ca460 (sb_writers#11){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
 #2: ffff888027ec9480 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
 #3: ffff88800bde95a8
 (kn->active#92){.+.+}-{0:0}
, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
, at: kernfs_fop_write_iter+0x332/0x5f0 fs/kernfs/file.c:337
 #4: ffff8880279cba40 (&q->rq_qos_mutex){+.+.}-{4:4}
, at: blkg_conf_open_bdev+0x253/0x410 block/blk-cgroup.c:800
 #5: 
ffff8880279cbbc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xbc/0xf10 block/blk-cgroup.c:843

stack backtrace:
CPU: 1 UID: 0 PID: 9684 Comm: syz.8.1099 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
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:2059
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
 check_prevs_add kernel/locking/lockdep.c:3300 [inline]
 validate_chain kernel/locking/lockdep.c:3924 [inline]
 __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
 lock_acquire kernel/locking/lockdep.c:5886 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bc0 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+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+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f30c299e0d9
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:00007f30c3858028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f30c2c25fa0 RCX: 00007f30c299e0d9
RDX: 000000000000006a RSI: 00002000000000c0 RDI: 0000000000000006
RBP: 00007f30c2a35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f30c2c26038 R14: 00007f30c2c25fa0 R15: 00007ffdf4eb11f8
 </TASK>