======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.0.5454/21421 is trying to acquire lock:
ffffffff90294f80 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline]
ffffffff90294f80 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x149/0x5f0 mm/page_alloc.c:5138

but task is already holding lock:
ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:635 [inline]
ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:568 [inline]
ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:628

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 mm/memory.c:7575
       _copy_from_iter+0x100/0x1680 lib/iov_iter.c:271
       copy_from_iter include/linux/uio.h:236 [inline]
       copy_from_iter_full include/linux/uio.h:253 [inline]
       skb_do_copy_data_nocache include/net/sock.h:2333 [inline]
       skb_copy_to_page_nocache include/net/sock.h:2359 [inline]
       tcp_sendmsg_locked+0x214a/0x53c0 net/ipv4/tcp.c:1321
       tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1462
       sock_sendmsg_nosec+0x10f/0x190 net/socket.c:801
       __sock_sendmsg net/socket.c:818 [inline]
       sock_write_iter+0x2de/0x3e0 net/socket.c:1269
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100 net/core/sock.c:3906
       lock_sock include/net/sock.h:1717 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:911
       nbd_mark_nsock_dead+0x2cb/0x550 drivers/block/nbd.c:319
       recv_work+0x1d14/0x1e30 drivers/block/nbd.c:1030
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x373/0xff0 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2141
       __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+0xd36/0x1580 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x167/0x2f0 block/blk-mq.c:2556
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       nbd_queue_rq+0xc1/0xff0 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2141
       __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+0xd36/0x1580 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x167/0x2f0 block/blk-mq.c:2556
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:261 [inline]
       __synchronize_srcu+0xca/0x2f0 kernel/rcu/srcutree.c:1662
       elevator_switch+0x1e8/0x7b0 block/elevator.c:576
       elevator_change+0x2fa/0x480 block/elevator.c:681
       elevator_set_default+0x375/0x440 block/elevator.c:754
       blk_register_queue+0x404/0x4f0 block/blk-sysfs.c:992
       __add_disk+0x6b8/0xdb0 block/genhd.c:531
       add_disk_fwnode+0x100/0x3a0 block/genhd.c:600
       add_disk include/linux/blkdev.h:799 [inline]
       nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2026
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743
       do_one_initcall+0x250/0x870 init/main.c:1419
       do_initcall_level+0x10a/0x1a0 init/main.c:1481
       do_initcalls+0x59/0xa0 init/main.c:1497
       kernel_init_freeable+0x29d/0x3e0 init/main.c:1732
       kernel_init+0x22/0x1d0 init/main.c:1622
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       elevator_change+0x1af/0x480 block/elevator.c:679
       elv_iosched_store+0x50e/0x630 block/elevator.c:831
       queue_attr_store+0x207/0x2b0 block/blk-sysfs.c:906
       kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}:
       blk_alloc_queue+0x544/0x690 block/blk-core.c:505
       blk_mq_alloc_queue block/blk-mq.c:4468 [inline]
       __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4515
       loop_add+0x480/0xb40 drivers/block/loop.c:1971
       loop_init+0xd7/0x160 drivers/block/loop.c:2210
       do_one_initcall+0x250/0x870 init/main.c:1419
       do_initcall_level+0x10a/0x1a0 init/main.c:1481
       do_initcalls+0x59/0xa0 init/main.c:1497
       kernel_init_freeable+0x29d/0x3e0 init/main.c:1732
       kernel_init+0x22/0x1d0 init/main.c:1622
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (fs_reclaim){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       __fs_reclaim_acquire mm/page_alloc.c:4365 [inline]
       fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4379
       might_alloc include/linux/sched/mm.h:316 [inline]
       prepare_alloc_pages+0x149/0x5f0 mm/page_alloc.c:5138
       __alloc_frozen_pages_noprof+0x17c/0x410 mm/page_alloc.c:5449
       alloc_pages_mpol+0x21e/0x390 mm/mempolicy.c:2511
       folio_alloc_mpol_noprof+0x39/0x160 mm/mempolicy.c:2530
       vma_alloc_folio_noprof+0xe1/0x1e0 mm/mempolicy.c:2565
       folio_prealloc mm/memory.c:-1 [inline]
       alloc_anon_folio mm/memory.c:5499 [inline]
       do_anonymous_page mm/memory.c:5594 [inline]
       do_pte_missing+0x16d4/0x3570 mm/memory.c:4776
       handle_pte_fault mm/memory.c:6665 [inline]
       __handle_mm_fault mm/memory.c:6817 [inline]
       handle_mm_fault+0x1807/0x2f80 mm/memory.c:6984
       do_user_addr_fault+0x7f6/0x1480 arch/x86/mm/fault.c:1394
       handle_page_fault arch/x86/mm/fault.c:1483 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
       stac arch/x86/include/asm/smap.h:-1 [inline]
       filldir64+0x294/0x690 fs/readdir.c:370
       dir_emit_dot include/linux/fs.h:3620 [inline]
       do_isofs_readdir fs/isofs/dir.c:157 [inline]
       isofs_readdir+0x687/0x1220 fs/isofs/dir.c:248
       iterate_dir+0x3db/0x880 fs/readdir.c:114
       __do_sys_getdents64 fs/readdir.c:404 [inline]
       __se_sys_getdents64+0xf1/0x280 fs/readdir.c:389
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       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.0.5454/21421: 3, on CPU#0:
 #0: ffff88802d3cb0b0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x118/0x160 fs/file.c:1409
 #1: ffff888054b9d070 (&type->i_mutex_dir_key#12){.+.+}-{4:4}, at: iterate_dir+0x287/0x880 fs/readdir.c:106
 #2: ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:635 [inline]
 #2: ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:568 [inline]
 #2: ffff8880262c4080 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:628

stack backtrace:
CPU: 0 UID: 0 PID: 21421 Comm: syz.0.5454 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __fs_reclaim_acquire mm/page_alloc.c:4365 [inline]
 fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4379
 might_alloc include/linux/sched/mm.h:316 [inline]
 prepare_alloc_pages+0x149/0x5f0 mm/page_alloc.c:5138
 __alloc_frozen_pages_noprof+0x17c/0x410 mm/page_alloc.c:5449
 alloc_pages_mpol+0x21e/0x390 mm/mempolicy.c:2511
 folio_alloc_mpol_noprof+0x39/0x160 mm/mempolicy.c:2530
 vma_alloc_folio_noprof+0xe1/0x1e0 mm/mempolicy.c:2565
 folio_prealloc mm/memory.c:-1 [inline]
 alloc_anon_folio mm/memory.c:5499 [inline]
 do_anonymous_page mm/memory.c:5594 [inline]
 do_pte_missing+0x16d4/0x3570 mm/memory.c:4776
 handle_pte_fault mm/memory.c:6665 [inline]
 __handle_mm_fault mm/memory.c:6817 [inline]
 handle_mm_fault+0x1807/0x2f80 mm/memory.c:6984
 do_user_addr_fault+0x7f6/0x1480 arch/x86/mm/fault.c:1394
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
RIP: 0010:filldir64+0x294/0x690 fs/readdir.c:372
Code: fd 48 29 d5 48 b8 00 f0 ff ff ff 7f 00 00 48 39 c5 48 0f 47 e8 bf 07 00 00 00 44 89 f6 e8 44 8e 6e ff 0f 01 cb 48 8b 44 24 58 <48> 89 45 08 48 8b 44 24 30 49 89 07 49 8d 47 10 48 bd 00 00 00 00
RSP: 0018:ffffc90004357c00 EFLAGS: 00050297
RAX: 0000000000000000 RBX: ffffc90004357e38 RCX: 0000000000000002
RDX: ffff888051f63e80 RSI: 0000000000000001 RDI: 0000000000000007
RBP: 0000200000002b00 R08: 00000000000005c0 R09: 0000000000000004
R10: 0000000000000001 R11: ffffffff825a9570 R12: ffffffff8c4a0520
R13: 0000000000000001 R14: 0000000000000001 R15: 0000200000002b00
 dir_emit_dot include/linux/fs.h:3620 [inline]
 do_isofs_readdir fs/isofs/dir.c:157 [inline]
 isofs_readdir+0x687/0x1220 fs/isofs/dir.c:248
 iterate_dir+0x3db/0x880 fs/readdir.c:114
 __do_sys_getdents64 fs/readdir.c:404 [inline]
 __se_sys_getdents64+0xf1/0x280 fs/readdir.c:389
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8b28fa8f19
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:00007f8b29ed7028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f8b29225fa0 RCX: 00007f8b28fa8f19
RDX: 0000000000001000 RSI: 0000200000002b00 RDI: 0000000000000004
RBP: 00007f8b29037f6d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8b29226038 R14: 00007f8b29225fa0 R15: 00007ffe17184658
 </TASK>
----------------
Code disassembly (best guess):
   0:	fd                   	std
   1:	48 29 d5             	sub    %rdx,%rbp
   4:	48 b8 00 f0 ff ff ff 	movabs $0x7ffffffff000,%rax
   b:	7f 00 00
   e:	48 39 c5             	cmp    %rax,%rbp
  11:	48 0f 47 e8          	cmova  %rax,%rbp
  15:	bf 07 00 00 00       	mov    $0x7,%edi
  1a:	44 89 f6             	mov    %r14d,%esi
  1d:	e8 44 8e 6e ff       	call   0xff6e8e66
  22:	0f 01 cb             	stac
  25:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
* 2a:	48 89 45 08          	mov    %rax,0x8(%rbp) <-- trapping instruction
  2e:	48 8b 44 24 30       	mov    0x30(%rsp),%rax
  33:	49 89 07             	mov    %rax,(%r15)
  36:	49 8d 47 10          	lea    0x10(%r15),%rax
  3a:	48                   	rex.W
  3b:	bd 00 00 00 00       	mov    $0x0,%ebp