======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.10683/9850 is trying to acquire lock:
ffffffff8ec848a0 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x61/0x660

but task is already holding lock:
ffff888172eb43e8 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}, at: unmap_vmas+0x36b/0x550

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #8 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}:
       down_write+0x96/0x200
       mmap_region+0x1d04/0x2310
       do_mmap+0xc3b/0x10c0
       vm_mmap_pgoff+0x272/0x4e0
       ksys_mmap_pgoff+0x57d/0x760
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #7 (&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+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100
       inet_shutdown+0x6a/0x390
       nbd_mark_nsock_dead+0x2cb/0x550
       recv_work+0x1cee/0x1e10
       process_scheduled_works+0xa8e/0x14e0
       worker_thread+0xa47/0xfb0
       kthread+0x388/0x470
       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+0xa8e/0x14e0
       worker_thread+0xa47/0xfb0
       kthread+0x388/0x470
       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+0xa8e/0x14e0
       worker_thread+0xa47/0xfb0
       kthread+0x388/0x470
       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+0x1d/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+0x7bb/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+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#51){++++}-{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+0x1d/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_cache_noprof+0x61/0x660
       allocate_file_region_entries+0x1ef/0x5a0
       __vma_reservation_common+0x7c2/0x9c0
       __unmap_hugepage_range+0x1032/0x1450
       __zap_vma_range+0x4de4/0x4f10
       unmap_vmas+0x390/0x550
       exit_mmap+0x293/0x9f0
       __mmput+0x118/0x420
       exit_mm+0x221/0x2d0
       do_exit+0x6cd/0x2360
       do_group_exit+0x22d/0x2f0
       get_signal+0x121b/0x12c0
       arch_do_signal_or_restart+0xbb/0x860
       exit_to_user_mode_loop+0x104/0x730
       do_syscall_64+0x353/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> &mm->mmap_lock --> &hugetlbfs_i_mmap_rwsem_key

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&hugetlbfs_i_mmap_rwsem_key);
                               lock(&mm->mmap_lock);
                               lock(&hugetlbfs_i_mmap_rwsem_key);
  lock(fs_reclaim);

 *** DEADLOCK ***

3 locks held by syz.0.10683/9850:
 #0: ffff8881769803b8 (&mm->mmap_lock){++++}-{4:4}, at: exit_mmap+0x1a4/0x9f0
 #1: ffff8881bdf75ce0 (&resv_map->rw_sema){++++}-{4:4}, at: __hugetlb_zap_begin+0x259/0x2d0
 #2: ffff888172eb43e8 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}, at: unmap_vmas+0x36b/0x550

stack backtrace:
CPU: 1 UID: 0 PID: 9850 Comm: syz.0.10683 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_cache_noprof+0x61/0x660
 allocate_file_region_entries+0x1ef/0x5a0
 __vma_reservation_common+0x7c2/0x9c0
 __unmap_hugepage_range+0x1032/0x1450
 __zap_vma_range+0x4de4/0x4f10
 unmap_vmas+0x390/0x550
 exit_mmap+0x293/0x9f0
 __mmput+0x118/0x420
 exit_mm+0x221/0x2d0
 do_exit+0x6cd/0x2360
 do_group_exit+0x22d/0x2f0
 get_signal+0x121b/0x12c0
 arch_do_signal_or_restart+0xbb/0x860
 exit_to_user_mode_loop+0x104/0x730
 do_syscall_64+0x353/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4aa1f9de99
Code: Unable to access opcode bytes at 0x7f4aa1f9de6f.
RSP: 002b:00007f4aa2d870e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f4aa2225fa8 RCX: 00007f4aa1f9de99
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f4aa2225fa8
RBP: 00007f4aa2225fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4aa2226038 R14: 00007ffea0e51d90 R15: 00007ffea0e51e78
 </TASK>
