======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.6956/22037 is trying to acquire lock:
ffffffff8ec8c680 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_noprof+0xbc/0x720

but task is already holding lock:
ffff88816af18fe0 (sk_lock-AF_INET6-NBD){+.+.}-{0:0}, at: tls_sw_sendmsg+0x15f/0x2b50

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (sk_lock-AF_INET6-NBD){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100
       inet_shutdown+0x6a/0x390
       nbd_mark_nsock_dead+0x2cb/0x550
       recv_work+0x1cee/0x1e10
       process_scheduled_works+0xa88/0x14c0
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       nbd_queue_rq+0x373/0x1150
       blk_mq_dispatch_rq_list+0x499/0x1990
       __blk_mq_sched_dispatch_requests+0xd36/0x1580
       blk_mq_sched_dispatch_requests+0xd7/0x190
       blk_mq_run_work_fn+0x16c/0x300
       process_scheduled_works+0xa88/0x14c0
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #4 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       nbd_queue_rq+0xc1/0x1150
       blk_mq_dispatch_rq_list+0x499/0x1990
       __blk_mq_sched_dispatch_requests+0xd36/0x1580
       blk_mq_sched_dispatch_requests+0xd7/0x190
       blk_mq_run_work_fn+0x16c/0x300
       process_scheduled_works+0xa88/0x14c0
       worker_thread+0xa47/0xfb0
       kthread+0x38b/0x480
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #3 (set->srcu){.+.+}-{0:0}:
       __synchronize_srcu+0xc9/0x2f0
       elevator_switch+0x1e8/0x7b0
       elevator_change+0x2fa/0x480
       elevator_set_default+0x375/0x440
       blk_register_queue+0x3f3/0x4e0
       __add_disk+0x6cb/0xe30
       add_disk_fwnode+0x100/0x3a0
       nbd_dev_add+0x733/0xb60
       nbd_init+0x15f/0x1e0
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x22/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       elevator_change+0x1af/0x480
       elevator_set_none+0xb5/0x140
       blk_mq_update_nr_hw_queues+0x5ef/0x19f0
       nbd_start_device+0x189/0xb30
       nbd_genl_connect+0x1597/0x1c10
       genl_family_rcv_msg_doit+0x233/0x340
       genl_rcv_msg+0x614/0x7a0
       netlink_rcv_skb+0x226/0x4a0
       genl_rcv+0x28/0x40
       netlink_unicast+0x7bd/0x940
       netlink_sendmsg+0x813/0xb40
       sock_sendmsg_nosec+0x13a/0x180
       ____sys_sendmsg+0x54e/0x850
       ___sys_sendmsg+0x2a5/0x360
       __x64_sys_sendmsg+0x1b1/0x290
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#50){++++}-{0:0}:
       blk_alloc_queue+0x544/0x690
       __blk_mq_alloc_disk+0x194/0x390
       nbd_dev_add+0x494/0xb60
       nbd_init+0x15f/0x1e0
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x22/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #0 (fs_reclaim){+.+.}-{0:0}:
       __lock_acquire+0x1520/0x2cf0
       lock_acquire+0x106/0x350
       fs_reclaim_acquire+0x71/0x100
       __kmalloc_noprof+0xbc/0x720
       tls_sw_sendmsg+0x59b/0x2b50
       sock_sendmsg_nosec+0x90/0x180
       sock_sendmsg+0x1ca/0x2d0
       splice_to_socket+0xb5e/0x12a0
       direct_splice_actor+0x101/0x160
       splice_direct_to_actor+0x57b/0xcb0
       do_splice_direct+0x195/0x290
       do_sendfile+0x52e/0x7c0
       __se_sys_sendfile64+0x144/0x1a0
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> &nsock->tx_lock --> sk_lock-AF_INET6-NBD

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET6-NBD);
                               lock(&nsock->tx_lock);
                               lock(sk_lock-AF_INET6-NBD);
  lock(fs_reclaim);

 *** DEADLOCK ***

locks held by syz.1.6956/22037: 2, last CPU#0:
 #0: ffff8881a118ace8 (&ctx->tx_lock){+.+.}-{4:4}, at: tls_sw_sendmsg+0x13a/0x2b50
 #1: ffff88816af18fe0 (sk_lock-AF_INET6-NBD){+.+.}-{0:0}, at: tls_sw_sendmsg+0x15f/0x2b50

stack backtrace:
CPU: 0 UID: 0 PID: 22037 Comm: syz.1.6956 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x1520/0x2cf0
 lock_acquire+0x106/0x350
 fs_reclaim_acquire+0x71/0x100
 __kmalloc_noprof+0xbc/0x720
 tls_sw_sendmsg+0x59b/0x2b50
 sock_sendmsg_nosec+0x90/0x180
 sock_sendmsg+0x1ca/0x2d0
 splice_to_socket+0xb5e/0x12a0
 direct_splice_actor+0x101/0x160
 splice_direct_to_actor+0x57b/0xcb0
 do_splice_direct+0x195/0x290
 do_sendfile+0x52e/0x7c0
 __se_sys_sendfile64+0x144/0x1a0
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7feece99e0d9
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:00007feecf7e9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007feecec26270 RCX: 00007feece99e0d9
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00007feecea35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000020000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007feecec26308 R14: 00007feecec26270 R15: 00007ffdf295a3c8
 </TASK>
