====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.1.17/3599 is trying to acquire lock: ffff88810aa9c698 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_elv_switch_none block/blk-mq.c:4942 [inline] ffff88810aa9c698 (&q->elevator_lock){+.+.}-{4:4}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5022 [inline] ffff88810aa9c698 (&q->elevator_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x190/0x500 block/blk-mq.c:5074 but task is already holding lock: ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave block/blk-mq.c:215 [inline] ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5014 [inline] ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: blk_mq_update_nr_hw_queues+0xbd/0x500 block/blk-mq.c:5074 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+0x317/0x360 block/blk-core.c:461 blk_mq_alloc_queue+0x61/0xd0 block/blk-mq.c:4349 __blk_mq_alloc_disk+0x13/0x60 block/blk-mq.c:4396 nbd_dev_add+0x1d0/0x3c0 drivers/block/nbd.c:1933 nbd_init+0xc4/0x170 drivers/block/nbd.c:2670 do_one_initcall+0x6f/0x340 init/main.c:1257 do_initcall_level init/main.c:1319 [inline] do_initcalls init/main.c:1335 [inline] do_basic_setup init/main.c:1354 [inline] kernel_init_freeable+0x23e/0x3f0 init/main.c:1568 kernel_init+0x15/0x1b0 init/main.c:1457 ret_from_fork+0x2c/0x50 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+0x98/0xd0 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+0x14c/0x470 block/blk-mq.c:4457 blk_mq_realloc_hw_ctxs+0x34c/0x400 block/blk-mq.c:4486 blk_mq_init_allocated_queue+0x105/0x4f0 block/blk-mq.c:4540 blk_mq_alloc_queue+0x7a/0xd0 block/blk-mq.c:4353 __blk_mq_alloc_disk+0x13/0x60 block/blk-mq.c:4396 loop_add+0x1f5/0x3e0 drivers/block/loop.c:2059 loop_init+0xb4/0x100 drivers/block/loop.c:2294 do_one_initcall+0x6f/0x340 init/main.c:1257 do_initcall_level init/main.c:1319 [inline] do_initcalls init/main.c:1335 [inline] do_basic_setup init/main.c:1354 [inline] kernel_init_freeable+0x23e/0x3f0 init/main.c:1568 kernel_init+0x15/0x1b0 init/main.c:1457 ret_from_fork+0x2c/0x50 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+0x1360/0x1ba0 kernel/locking/lockdep.c:5228 lock_acquire kernel/locking/lockdep.c:5851 [inline] lock_acquire+0xce/0x2d0 kernel/locking/lockdep.c:5816 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0xc6/0xa90 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+0x190/0x500 block/blk-mq.c:5074 nbd_start_device+0x56/0x3c0 drivers/block/nbd.c:1476 nbd_genl_connect+0x372/0x860 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0xfb/0x160 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x1b7/0x2d0 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x53/0x100 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+0x1cf/0x2c0 net/netlink/af_netlink.c:1348 netlink_sendmsg+0x217/0x460 net/netlink/af_netlink.c:1892 sock_sendmsg_nosec net/socket.c:718 [inline] __sock_sendmsg net/socket.c:733 [inline] ____sys_sendmsg+0x35e/0x390 net/socket.c:2573 ___sys_sendmsg+0x95/0xe0 net/socket.c:2627 __sys_sendmsg+0x82/0xe0 net/socket.c:2659 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x80/0x1b0 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.1.17/3599: #0: ffffffff84805350 (cb_lock){++++}-{4:4}, at: genl_rcv+0x14/0x30 net/netlink/genetlink.c:1218 #1: ffffffff848053e8 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline] #1: ffffffff848053e8 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline] #1: ffffffff848053e8 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:57 [inline] #1: ffffffff848053e8 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x1e0/0x2d0 net/netlink/genetlink.c:1209 #2: ffff88810c29d598 (&nbd->config_lock){+.+.}-{4:4}, at: nbd_genl_connect+0x454/0x860 drivers/block/nbd.c:2111 #3: ffff88810c29d4d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0x3c/0x500 block/blk-mq.c:5073 #4: ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: blk_mq_freeze_queue_nomemsave block/blk-mq.c:215 [inline] #4: ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5014 [inline] #4: ffff88810aa9c168 (&q->q_usage_counter(io)#49){++++}-{0:0}, at: blk_mq_update_nr_hw_queues+0xbd/0x500 block/blk-mq.c:5074 #5: ffff88810aa9c1a0 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: blk_mq_freeze_queue_nomemsave block/blk-mq.c:215 [inline] #5: ffff88810aa9c1a0 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: __blk_mq_update_nr_hw_queues block/blk-mq.c:5014 [inline] #5: ffff88810aa9c1a0 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: blk_mq_update_nr_hw_queues+0xbd/0x500 block/blk-mq.c:5074 stack backtrace: CPU: 1 UID: 0 PID: 3599 Comm: syz.1.17 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x78/0xe0 lib/dump_stack.c:120 print_circular_bug+0x26e/0x2f0 kernel/locking/lockdep.c:2076 check_noncircular+0x11d/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+0x1360/0x1ba0 kernel/locking/lockdep.c:5228 lock_acquire kernel/locking/lockdep.c:5851 [inline] lock_acquire+0xce/0x2d0 kernel/locking/lockdep.c:5816 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0xc6/0xa90 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+0x190/0x500 block/blk-mq.c:5074 nbd_start_device+0x56/0x3c0 drivers/block/nbd.c:1476 nbd_genl_connect+0x372/0x860 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0xfb/0x160 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x1b7/0x2d0 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x53/0x100 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+0x1cf/0x2c0 net/netlink/af_netlink.c:1348 netlink_sendmsg+0x217/0x460 net/netlink/af_netlink.c:1892 sock_sendmsg_nosec net/socket.c:718 [inline] __sock_sendmsg net/socket.c:733 [inline] ____sys_sendmsg+0x35e/0x390 net/socket.c:2573 ___sys_sendmsg+0x95/0xe0 net/socket.c:2627 __sys_sendmsg+0x82/0xe0 net/socket.c:2659 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x80/0x1b0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f65cf38eba9 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:00007f65d0203038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f65cf5d5fa0 RCX: 00007f65cf38eba9 RDX: 0000000000004000 RSI: 00002000000027c0 RDI: 0000000000000005 RBP: 00007f65cf411e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f65cf5d6038 R14: 00007f65cf5d5fa0 R15: 00007ffdf9454228 nbd0: detected capacity change from 0 to 32