====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.2.17/3343 is trying to acquire lock: ffff888108ad6b98 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_elv_switch_none block/blk-mq.c:4942 [inline] ffff888108ad6b98 (&q->elevator_lock){+.+.}-{4:4}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5022 [inline] ffff888108ad6b98 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x1d2/0x690 block/blk-mq.c:5074 but task is already holding lock: ffff888108ad6668 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x5e/0x3a0 drivers/block/nbd.c:1476 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}: blk_alloc_queue+0x33f/0x370 block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4349 [inline] __blk_mq_alloc_disk+0x74/0x120 block/blk-mq.c:4396 nbd_dev_add+0x1f0/0x390 drivers/block/nbd.c:1933 nbd_init+0x146/0x160 drivers/block/nbd.c:2670 do_one_initcall+0xe3/0x380 init/main.c:1257 do_initcall_level+0x8f/0x100 init/main.c:1319 do_initcalls+0x54/0x90 init/main.c:1335 kernel_init_freeable+0x183/0x1f0 init/main.c:1568 kernel_init+0x15/0x120 init/main.c:1457 ret_from_fork+0x32/0x40 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 -> #1 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:3853 [inline] fs_reclaim_acquire+0x51/0xc0 mm/page_alloc.c:3867 might_alloc include/linux/sched/mm.h:318 [inline] xa_insert include/linux/xarray.h:783 [inline] blk_mq_init_hctx block/blk-mq.c:3924 [inline] blk_mq_alloc_and_init_hctx+0x361/0x430 block/blk-mq.c:4457 blk_mq_realloc_hw_ctxs+0x62/0x3f0 block/blk-mq.c:4486 blk_mq_init_allocated_queue+0x148/0x540 block/blk-mq.c:4540 blk_mq_alloc_queue block/blk-mq.c:4353 [inline] __blk_mq_alloc_disk+0x8d/0x120 block/blk-mq.c:4396 loop_add+0x1d4/0x3d0 drivers/block/loop.c:2059 loop_init+0xc2/0xe0 drivers/block/loop.c:2294 do_one_initcall+0xe3/0x380 init/main.c:1257 do_initcall_level+0x8f/0x100 init/main.c:1319 do_initcalls+0x54/0x90 init/main.c:1335 kernel_init_freeable+0x183/0x1f0 init/main.c:1568 kernel_init+0x15/0x120 init/main.c:1457 ret_from_fork+0x32/0x40 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 -> #0 (&q->elevator_lock){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain kernel/locking/lockdep.c:3906 [inline] __lock_acquire+0x12cb/0x20e0 kernel/locking/lockdep.c:5228 lock_acquire+0xea/0x270 kernel/locking/lockdep.c:5851 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0xac/0xa90 kernel/locking/mutex.c:730 blk_mq_elv_switch_none block/blk-mq.c:4942 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5022 [inline] blk_mq_update_nr_hw_queues+0x1d2/0x690 block/blk-mq.c:5074 nbd_start_device+0x5e/0x3a0 drivers/block/nbd.c:1476 nbd_genl_connect+0x644/0x8c0 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0xed/0x140 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x239/0x250 net/netlink/genetlink.c:1210 netlink_rcv_skb+0xe6/0x120 net/netlink/af_netlink.c:2543 genl_rcv+0x23/0x30 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline] netlink_unicast+0x1e9/0x300 net/netlink/af_netlink.c:1348 netlink_sendmsg+0x33d/0x3d0 net/netlink/af_netlink.c:1892 sock_sendmsg_nosec net/socket.c:718 [inline] __sock_sendmsg+0x81/0xa0 net/socket.c:733 ____sys_sendmsg+0x1bb/0x210 net/socket.c:2573 ___sys_sendmsg+0x28a/0x2d0 net/socket.c:2627 __sys_sendmsg net/socket.c:2659 [inline] __do_sys_sendmsg net/socket.c:2664 [inline] __se_sys_sendmsg net/socket.c:2662 [inline] __x64_sys_sendmsg+0xea/0x140 net/socket.c:2662 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xa4/0x180 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &q->elevator_lock --> fs_reclaim --> &q->q_usage_counter(io)#49 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#49); lock(fs_reclaim); lock(&q->q_usage_counter(io)#49); lock(&q->elevator_lock); *** DEADLOCK *** 6 locks held by syz.2.17/3343: #0: ffffffff83d30600 (cb_lock){++++}-{4:4}, at: genl_rcv+0x14/0x30 net/netlink/genetlink.c:1218 #1: ffffffff83d304d8 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline] #1: ffffffff83d304d8 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline] #1: ffffffff83d304d8 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x59/0x250 net/netlink/genetlink.c:1209 #2: ffff8881092c4198 (&nbd->config_lock){+.+.}-{4:4}, at: nbd_genl_connect+0x2f4/0x8c0 drivers/block/nbd.c:2111 #3: ffff8881092c40d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x35/0x690 block/blk-mq.c:5073 #4: ffff888108ad6668 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: nbd_start_device+0x5e/0x3a0 drivers/block/nbd.c:1476 #5: ffff888108ad66a0 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: nbd_start_device+0x5e/0x3a0 drivers/block/nbd.c:1476 stack backtrace: CPU: 1 UID: 0 PID: 3343 Comm: syz.2.17 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: dump_stack_lvl+0xaf/0x110 lib/dump_stack.c:120 print_circular_bug+0x29b/0x2b0 kernel/locking/lockdep.c:2076 check_noncircular+0x110/0x130 kernel/locking/lockdep.c:2208 check_prev_add kernel/locking/lockdep.c:3163 [inline] check_prevs_add kernel/locking/lockdep.c:3282 [inline] validate_chain kernel/locking/lockdep.c:3906 [inline] __lock_acquire+0x12cb/0x20e0 kernel/locking/lockdep.c:5228 lock_acquire+0xea/0x270 kernel/locking/lockdep.c:5851 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0xac/0xa90 kernel/locking/mutex.c:730 blk_mq_elv_switch_none block/blk-mq.c:4942 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5022 [inline] blk_mq_update_nr_hw_queues+0x1d2/0x690 block/blk-mq.c:5074 nbd_start_device+0x5e/0x3a0 drivers/block/nbd.c:1476 nbd_genl_connect+0x644/0x8c0 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0xed/0x140 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x239/0x250 net/netlink/genetlink.c:1210 netlink_rcv_skb+0xe6/0x120 net/netlink/af_netlink.c:2543 genl_rcv+0x23/0x30 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline] netlink_unicast+0x1e9/0x300 net/netlink/af_netlink.c:1348 netlink_sendmsg+0x33d/0x3d0 net/netlink/af_netlink.c:1892 sock_sendmsg_nosec net/socket.c:718 [inline] __sock_sendmsg+0x81/0xa0 net/socket.c:733 ____sys_sendmsg+0x1bb/0x210 net/socket.c:2573 ___sys_sendmsg+0x28a/0x2d0 net/socket.c:2627 __sys_sendmsg net/socket.c:2659 [inline] __do_sys_sendmsg net/socket.c:2664 [inline] __se_sys_sendmsg net/socket.c:2662 [inline] __x64_sys_sendmsg+0xea/0x140 net/socket.c:2662 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xa4/0x180 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fd6a078ebe9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fd69fdfe038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007fd6a09c5fa0 RCX: 00007fd6a078ebe9 RDX: 0000000000000800 RSI: 0000200000001ac0 RDI: 0000000000000005 RBP: 00007fd6a0811e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fd6a09c6038 R14: 00007fd6a09c5fa0 R15: 00007ffc9235a2c8 nbd0: detected capacity change from 0 to 127