======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.8470/7425 is trying to acquire lock:
ffffffff90094cc0 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x149/0x5f0

but task is already holding lock:
ffff88803605f180 (&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:

-> #7 (&mm->mmap_lock){++++}-{4:4}:
       __might_fault+0xcb/0x130
       _copy_from_iter+0x100/0x1680
       tcp_sendmsg_locked+0x214a/0x53c0
       tcp_sendmsg+0x2f/0x50
       sock_sendmsg_nosec+0x10f/0x190
       sock_write_iter+0x2de/0x3e0
       vfs_write+0x612/0xba0
       ksys_write+0x150/0x270
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100
       inet_shutdown+0x6a/0x390
       nbd_mark_nsock_dead+0x2cb/0x550
       recv_work+0x1d14/0x1e30
       process_scheduled_works+0xc3d/0x1630
       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+0x197/0x15a0
       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+0x167/0x2f0
       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+0x197/0x15a0
       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+0x167/0x2f0
       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+0xca/0x2f0
       elevator_switch+0x1e8/0x7b0
       elevator_change+0x2fa/0x480
       elevator_set_default+0x375/0x440
       blk_register_queue+0x404/0x4f0
       __add_disk+0x6b8/0xdb0
       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+0x197/0x15a0
       elevator_change+0x1af/0x480
       elevator_set_none+0xb5/0x140
       blk_mq_update_nr_hw_queues+0x5ef/0x19e0
       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+0x8ef/0xa80
       netlink_sendmsg+0x7f0/0xb20
       sock_sendmsg_nosec+0x14e/0x190
       ____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)#49){++++}-{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+0x164c/0x2de0
       lock_acquire+0x115/0x350
       fs_reclaim_acquire+0x71/0x100
       prepare_alloc_pages+0x149/0x5f0
       __alloc_frozen_pages_noprof+0x17c/0x410
       alloc_pages_mpol+0x21e/0x390
       folio_alloc_mpol_noprof+0x39/0x160
       vma_alloc_folio_noprof+0xe1/0x1e0
       do_pte_missing+0x16d4/0x3570
       handle_mm_fault+0x1a53/0x3750
       do_user_addr_fault+0x7f6/0x1480
       exc_page_fault+0x6a/0xc0
       asm_exc_page_fault+0x26/0x30
       __put_user_4+0xd/0x30
       pppox_ioctl+0x1de/0x3f0
       sock_do_ioctl+0x101/0x320
       sock_ioctl+0x57a/0x7e0
       __se_sys_ioctl+0xfc/0x170
       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_INET --> &mm->mmap_lock

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

locks held by syz.3.8470/7425: 2, last CPU#1:
 #0: ffff8881a72f0260 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppox_ioctl+0x4d/0x3f0
 #1: ffff88803605f180 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340

stack backtrace:
CPU: 1 UID: 0 PID: 7425 Comm: syz.3.8470 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+0x164c/0x2de0
 lock_acquire+0x115/0x350
 fs_reclaim_acquire+0x71/0x100
 prepare_alloc_pages+0x149/0x5f0
 __alloc_frozen_pages_noprof+0x17c/0x410
 alloc_pages_mpol+0x21e/0x390
 folio_alloc_mpol_noprof+0x39/0x160
 vma_alloc_folio_noprof+0xe1/0x1e0
 do_pte_missing+0x16d4/0x3570
 handle_mm_fault+0x1a53/0x3750
 do_user_addr_fault+0x7f6/0x1480
 exc_page_fault+0x6a/0xc0
 asm_exc_page_fault+0x26/0x30
RIP: 0010:__put_user_4+0xd/0x30
Code: 1f 00 c3 cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 48 89 cb 48 c1 fb 3f 48 09 d9 0f 1f 00 <89> 01 31 c9 0f 1f 00 c3 cc cc cc cc 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc900063a7c78 EFLAGS: 00010202
RAX: 0000000000000015 RBX: 0000000000000000 RCX: 0000200000001280
RDX: 00000000882354b0 RSI: ffffffff8e92d82e RDI: ffffffff8c8e8c80
RBP: 0000000000000015 R08: ffffffff822670ef R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff233ae78 R12: 0000200000001280
R13: 1ffff11034e5e002 R14: ffff8881a72f0000 R15: dffffc0000000000
 pppox_ioctl+0x1de/0x3f0
 sock_do_ioctl+0x101/0x320
 sock_ioctl+0x57a/0x7e0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd4bf59f559
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:00007fd4c040e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd4bf826090 RCX: 00007fd4bf59f559
RDX: 0000200000001280 RSI: 0000000080047437 RDI: 0000000000000007
RBP: 00007fd4bf636b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd4bf826128 R14: 00007fd4bf826090 R15: 00007ffe83311438
 </TASK>
