======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.21321/28265 is trying to acquire lock:
ffffffff8ee8f980 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x149/0x600

but task is already holding lock:
ffff88811277b6b8 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #8 (&mm->mmap_lock){++++}-{4:4}:
       __might_fault+0xcb/0x130
       _copy_from_user+0x28/0xb0
       csum_and_copy_from_iter_full+0x210/0x1fb0
       ip_generic_getfrag+0x149/0x2d0
       __ip6_append_data+0x3b26/0x40c0
       ip6_append_data+0x108/0x270
       rawv6_sendmsg+0x1298/0x18c0
       sock_sendmsg_nosec+0x10e/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

-> #7 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100
       tls_sw_sendmsg+0x15f/0x2b50
       sock_sendmsg_nosec+0x90/0x180
       sock_write_iter+0x2de/0x3e0
       do_iter_readv_writev+0x612/0x8c0
       vfs_writev+0x343/0x990
       do_writev+0x154/0x2e0
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (&ctx->tx_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       tls_sw_sendmsg+0x13a/0x2b50
       sock_sendmsg_nosec+0x90/0x180
       sock_sendmsg+0x1ca/0x2d0
       __sock_xmit+0x245/0x4f0
       nbd_disconnect+0x3ad/0x560
       nbd_disconnect_and_put+0x32/0x280
       nbd_genl_disconnect+0x4af/0x590
       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

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       nbd_queue_rq+0x373/0xff0
       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+0xc3d/0x1630
       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+0xc1/0xff0
       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+0xc3d/0x1630
       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+0x168/0x1f0
       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+0x167d/0x1cd0
       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+0x168/0x1f0
       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+0x15ff/0x2e50
       lock_acquire+0x115/0x350
       fs_reclaim_acquire+0x71/0x100
       prepare_alloc_pages+0x149/0x600
       __alloc_frozen_pages_noprof+0x185/0x5a0
       alloc_pages_mpol+0x21e/0x390
       folio_alloc_mpol_noprof+0x39/0x160
       vma_alloc_folio_noprof+0xe1/0x1e0
       do_pte_missing+0x173a/0x34b0
       handle_mm_fault+0x1a53/0x3750
       do_user_addr_fault+0x746/0x1340
       exc_page_fault+0x6a/0xc0
       asm_exc_page_fault+0x26/0x30
       rep_movs_alternative+0x54/0xa0
       _copy_to_user+0x8a/0xb0
       do_ipt_get_ctl+0xcae/0x1300
       nf_getsockopt+0x26e/0x290
       ip_getsockopt+0x19e/0x230
       udp_getsockopt+0x138/0x2d0
       do_sock_getsockopt+0x51d/0x7e0
       __x64_sys_getsockopt+0x1a4/0x240
       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 --> sk_lock-AF_INET6 --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&mm->mmap_lock);
                               lock(sk_lock-AF_INET6);
                               lock(&mm->mmap_lock);
  lock(fs_reclaim);

 *** DEADLOCK ***

locks held by syz.3.21321/28265: 2, last CPU#0:
 #0: ffff888177abc2e0 (&xt[i].mutex){+.+.}-{4:4}, at: xt_find_table_lock+0x55/0x400
 #1: ffff88811277b6b8 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340

stack backtrace:
CPU: 0 UID: 0 PID: 28265 Comm: syz.3.21321 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+0x2e2/0x300
 check_noncircular+0x12f/0x150
 __lock_acquire+0x15ff/0x2e50
 lock_acquire+0x115/0x350
 fs_reclaim_acquire+0x71/0x100
 prepare_alloc_pages+0x149/0x600
 __alloc_frozen_pages_noprof+0x185/0x5a0
 alloc_pages_mpol+0x21e/0x390
 folio_alloc_mpol_noprof+0x39/0x160
 vma_alloc_folio_noprof+0xe1/0x1e0
 do_pte_missing+0x173a/0x34b0
 handle_mm_fault+0x1a53/0x3750
 do_user_addr_fault+0x746/0x1340
 exc_page_fault+0x6a/0xc0
 asm_exc_page_fault+0x26/0x30
RIP: 0010:rep_movs_alternative+0x54/0xa0
Code: 00 00 00 0f 1f 00 48 8b 06 48 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 db 83 f9 08 73 e8 eb c5 eb 05 e9 4f 66 04 00 48 8b 06 <48> 89 07 48 8d 47 08 48 83 e0 f8 48 29 f8 48 01 c7 48 01 c6 48 29
RSP: 0018:ffffc900247376e8 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000000000060 RCX: 0000000000000060
RDX: 0000000000000000 RSI: ffff88810ccd50d8 RDI: 0000200000001000
RBP: ffffc90024737a78 R08: ffff88810ccd5137 R09: 1ffff1102199aa26
R10: dffffc0000000000 R11: ffffed102199aa27 R12: 0000200000001060
R13: 00007ffffffff000 R14: ffff88810ccd50d8 R15: 0000200000001000
 _copy_to_user+0x8a/0xb0
 do_ipt_get_ctl+0xcae/0x1300
 nf_getsockopt+0x26e/0x290
 ip_getsockopt+0x19e/0x230
 udp_getsockopt+0x138/0x2d0
 do_sock_getsockopt+0x51d/0x7e0
 __x64_sys_getsockopt+0x1a4/0x240
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f799819e159
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:00007f7998fa9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007f7998425fa0 RCX: 00007f799819e159
RDX: 0000000000000041 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f7998235024 R08: 0000200000000300 R09: 0000000000000000
R10: 0000200000000f40 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7998426038 R14: 00007f7998425fa0 R15: 00007ffe3716cab8
 </TASK>
