======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G        W    L     
------------------------------------------------------
kworker/0:0H/11 is trying to acquire lock:
ffff800087b74020 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline]
ffff800087b74020 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline]
ffff800087b74020 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline]
ffff800087b74020 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_node_noprof+0x6c/0x634 mm/slub.c:5578

but task is already holding lock:
ffff000014f95080 (&new->lock){+.+.}-{4:4}, at: mtd_blktrans_work drivers/mtd/mtd_blkdevs.c:151 [inline]
ffff000014f95080 (&new->lock){+.+.}-{4:4}, at: mtd_queue_rq+0x2a4/0x1694 drivers/mtd/mtd_blkdevs.c:179

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&new->lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x3d0/0x44c kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x150/0x1530 kernel/locking/mutex.c:821
       mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
       mtd_blktrans_work drivers/mtd/mtd_blkdevs.c:151 [inline]
       mtd_queue_rq+0x2a4/0x1694 drivers/mtd/mtd_blkdevs.c:179
       blk_mq_dispatch_rq_list+0x2e0/0x177c block/blk-mq.c:2117
       __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+0x830/0xe60 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0x7c/0x114 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0xf0/0x278 block/blk-mq.c:2531
       process_one_work+0x830/0x1c00 kernel/workqueue.c:3387
       process_scheduled_works kernel/workqueue.c:3470 [inline]
       worker_thread+0x42c/0xc90 kernel/workqueue.c:3551
       kthread+0x2ec/0x384 kernel/kthread.c:436
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

-> #3 (set->srcu){.+.+}-{0:0}:
       lock_sync+0xf0/0x16c kernel/locking/lockdep.c:5934
       srcu_lock_sync include/linux/srcu.h:210 [inline]
       __synchronize_srcu+0xa8/0x280 kernel/rcu/srcutree.c:1462
       synchronize_srcu_expedited kernel/rcu/srcutree.c:1502 [inline]
       synchronize_srcu+0x168/0x7d0 kernel/rcu/srcutree.c:1558
       blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
       blk_mq_quiesce_queue+0xf4/0x160 block/blk-mq.c:299
       elevator_switch+0x118/0x430 block/elevator.c:576
       elevator_change+0x294/0x420 block/elevator.c:681
       elevator_set_default+0x210/0x2b8 block/elevator.c:754
       blk_register_queue+0x36c/0x500 block/blk-sysfs.c:992
       __add_disk+0x510/0xb48 block/genhd.c:524
       add_disk_fwnode+0x110/0x3e0 block/genhd.c:593
       device_add_disk+0x14/0x20 block/genhd.c:623
       add_disk include/linux/blkdev.h:798 [inline]
       nbd_dev_add+0x5f8/0x9b4 drivers/block/nbd.c:2026
       nbd_init+0x190/0x1b0 drivers/block/nbd.c:2743
       do_one_initcall+0x134/0xb20 init/main.c:1357
       do_initcall_level init/main.c:1419 [inline]
       do_initcalls init/main.c:1435 [inline]
       do_basic_setup init/main.c:1455 [inline]
       kernel_init_freeable+0x5ec/0x670 init/main.c:1670
       kernel_init+0x2c/0x14c init/main.c:1560
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x3d0/0x44c kernel/locking/lockdep.c:5843
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x150/0x1530 kernel/locking/mutex.c:821
       mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
       elevator_change+0x188/0x420 block/elevator.c:679
       elevator_set_none+0x90/0xec block/elevator.c:769
       blk_mq_elv_switch_none block/blk-mq.c:5102 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline]
       blk_mq_update_nr_hw_queues+0x3c0/0x1020 block/blk-mq.c:5212
       nbd_start_device+0x128/0xa28 drivers/block/nbd.c:1530
       nbd_genl_connect+0xb50/0x1394 drivers/block/nbd.c:2310
       genl_family_rcv_msg_doit+0x1c0/0x28c net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x3f8/0x60c net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x1ac/0x360 net/netlink/af_netlink.c:2556
       genl_rcv+0x38/0x54 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x418/0x6e0 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x638/0xa4c net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec net/socket.c:800 [inline]
       __sock_sendmsg+0xc8/0x1a4 net/socket.c:815
       ____sys_sendmsg+0x52c/0x76c net/socket.c:2713
       ___sys_sendmsg+0x124/0x1a4 net/socket.c:2767
       __sys_sendmsg+0x10c/0x198 net/socket.c:2799
       __compat_sys_sendmsg net/compat.c:345 [inline]
       __do_compat_sys_sendmsg net/compat.c:352 [inline]
       __se_compat_sys_sendmsg net/compat.c:349 [inline]
       __arm64_compat_sys_sendmsg+0x74/0xa4 net/compat.c:349
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x74/0x240 arch/arm64/kernel/syscall.c:49
       el0_svc_common.constprop.0+0xac/0x230 arch/arm64/kernel/syscall.c:121
       do_el0_svc_compat+0x40/0x58 arch/arm64/kernel/syscall.c:146
       el0_svc_compat+0x54/0x264 arch/arm64/kernel/entry-common.c:909
       el0t_32_sync_handler+0x88/0xac arch/arm64/kernel/entry-common.c:927
       el0t_32_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:595

-> #1 (&q->q_usage_counter(io)#33){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x3d0/0x44c kernel/locking/lockdep.c:5843
       blk_alloc_queue+0x4e0/0x640 block/blk-core.c:504
       blk_mq_alloc_queue+0x148/0x224 block/blk-mq.c:4420
       __blk_mq_alloc_disk+0x20/0x120 block/blk-mq.c:4467
       nbd_dev_add+0x3d0/0x9b4 drivers/block/nbd.c:1996
       nbd_init+0x190/0x1b0 drivers/block/nbd.c:2743
       do_one_initcall+0x134/0xb20 init/main.c:1357
       do_initcall_level init/main.c:1419 [inline]
       do_initcalls init/main.c:1435 [inline]
       do_basic_setup init/main.c:1455 [inline]
       kernel_init_freeable+0x5ec/0x670 init/main.c:1670
       kernel_init+0x2c/0x14c init/main.c:1560
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

-> #0 (fs_reclaim){+.+.}-{0:0}:
       check_prev_add+0x114/0xca0 kernel/locking/lockdep.c:3181
       check_prevs_add kernel/locking/lockdep.c:3300 [inline]
       validate_chain kernel/locking/lockdep.c:3924 [inline]
       __lock_acquire+0x13f4/0x1a5c kernel/locking/lockdep.c:5253
       lock_acquire kernel/locking/lockdep.c:5886 [inline]
       lock_acquire+0x3d0/0x44c kernel/locking/lockdep.c:5843
       __fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
       fs_reclaim_acquire+0x130/0x158 mm/page_alloc.c:4389
       might_alloc include/linux/sched/mm.h:316 [inline]
       slab_pre_alloc_hook mm/slub.c:4636 [inline]
       slab_alloc_node mm/slub.c:4974 [inline]
       __kmalloc_cache_node_noprof+0x6c/0x634 mm/slub.c:5578
       _kmalloc_node_noprof include/linux/slab.h:1196 [inline]
       __get_vm_area_node+0x118/0x2ec mm/vmalloc.c:3238
       __vmalloc_node_range_noprof+0x198/0x1024 mm/vmalloc.c:4065
       __vmalloc_node_noprof+0xe4/0x14c mm/vmalloc.c:4166
       vmalloc_noprof+0x24/0x30 mm/vmalloc.c:4201
       mtdblock_writesect+0x41c/0x5b8 drivers/mtd/mtdblock.c:242
       do_blktrans_request drivers/mtd/mtd_blkdevs.c:88 [inline]
       mtd_blktrans_work drivers/mtd/mtd_blkdevs.c:152 [inline]
       mtd_queue_rq+0x744/0x1694 drivers/mtd/mtd_blkdevs.c:179
       blk_mq_dispatch_rq_list+0x2e0/0x177c block/blk-mq.c:2117
       __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+0x830/0xe60 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0x7c/0x114 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0xf0/0x278 block/blk-mq.c:2531
       process_one_work+0x830/0x1c00 kernel/workqueue.c:3387
       process_scheduled_works kernel/workqueue.c:3470 [inline]
       worker_thread+0x42c/0xc90 kernel/workqueue.c:3551
       kthread+0x2ec/0x384 kernel/kthread.c:436
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> set->srcu --> &new->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&new->lock);
                               lock(set->srcu);
                               lock(&new->lock);
  lock(fs_reclaim);

 *** DEADLOCK ***

locks held by kworker/0:0H/11: 4, last CPU#0:
 #0: ffff00000ed7c140 ((wq_completion)kblockd){+.+.}-{0:0}, at: process_one_work+0x12ec/0x1c00 kernel/workqueue.c:3362
 #1: ffff80008dc97c70 ((work_completion)(&(&hctx->run_work)->work)){+.+.}-{0:0}, at: process_one_work+0x780/0x1c00 kernel/workqueue.c:3361
 #2: ffff000014cce818 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:304 [inline]
 #2: ffff000014cce818 (set->srcu){.+.+}-{0:0}, at: blk_mq_run_work_fn+0xc8/0x278 block/blk-mq.c:2531
 #3: ffff000014f95080 (&new->lock){+.+.}-{4:4}, at: mtd_blktrans_work drivers/mtd/mtd_blkdevs.c:151 [inline]
 #3: ffff000014f95080 (&new->lock){+.+.}-{4:4}, at: mtd_queue_rq+0x2a4/0x1694 drivers/mtd/mtd_blkdevs.c:179

stack backtrace:
CPU: 0 UID: 0 PID: 11 Comm: kworker/0:0H Tainted: G        W    L      syzkaller #0 PREEMPT 
Tainted: [W]=WARN, [L]=SOFTLOCKUP
Hardware name: linux,dummy-virt (DT)
Workqueue: kblockd blk_mq_run_work_fn
Call trace:
 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x7c/0xb0 lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x23c/0x284 kernel/locking/lockdep.c:2059
 check_noncircular+0x174/0x194 kernel/locking/lockdep.c:2191
 check_prev_add+0x114/0xca0 kernel/locking/lockdep.c:3181
 check_prevs_add kernel/locking/lockdep.c:3300 [inline]
 validate_chain kernel/locking/lockdep.c:3924 [inline]
 __lock_acquire+0x13f4/0x1a5c kernel/locking/lockdep.c:5253
 lock_acquire kernel/locking/lockdep.c:5886 [inline]
 lock_acquire+0x3d0/0x44c kernel/locking/lockdep.c:5843
 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
 fs_reclaim_acquire+0x130/0x158 mm/page_alloc.c:4389
 might_alloc include/linux/sched/mm.h:316 [inline]
 slab_pre_alloc_hook mm/slub.c:4636 [inline]
 slab_alloc_node mm/slub.c:4974 [inline]
 __kmalloc_cache_node_noprof+0x6c/0x634 mm/slub.c:5578
 _kmalloc_node_noprof include/linux/slab.h:1196 [inline]
 __get_vm_area_node+0x118/0x2ec mm/vmalloc.c:3238
 __vmalloc_node_range_noprof+0x198/0x1024 mm/vmalloc.c:4065
 __vmalloc_node_noprof+0xe4/0x14c mm/vmalloc.c:4166
 vmalloc_noprof+0x24/0x30 mm/vmalloc.c:4201
 mtdblock_writesect+0x41c/0x5b8 drivers/mtd/mtdblock.c:242
 do_blktrans_request drivers/mtd/mtd_blkdevs.c:88 [inline]
 mtd_blktrans_work drivers/mtd/mtd_blkdevs.c:152 [inline]
 mtd_queue_rq+0x744/0x1694 drivers/mtd/mtd_blkdevs.c:179
 blk_mq_dispatch_rq_list+0x2e0/0x177c block/blk-mq.c:2117
 __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+0x830/0xe60 block/blk-mq-sched.c:307
 blk_mq_sched_dispatch_requests+0x7c/0x114 block/blk-mq-sched.c:329
 blk_mq_run_work_fn+0xf0/0x278 block/blk-mq.c:2531
 process_one_work+0x830/0x1c00 kernel/workqueue.c:3387
 process_scheduled_works kernel/workqueue.c:3470 [inline]
 worker_thread+0x42c/0xc90 kernel/workqueue.c:3551
 kthread+0x2ec/0x384 kernel/kthread.c:436
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854