syzbot

 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
======================================================
WARNING: possible circular locking dependency detected
6.1.123-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor958/4311 is trying to acquire lock:
ffff0000d00190a8 ((&sq->pending_timer)){+.-.}-{0:0}, at: timer_delete_sync+0x74/0x210 kernel/time/timer.c:1448

but task is already holding lock:
ffff80001ce537b0 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff80001ce537b0 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ac/0x4a8 block/blk-cgroup.c:1493

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&blkcg->lock){....}-{2:2}:
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x54/0x6c kernel/locking/spinlock.c:154
       spin_lock include/linux/spinlock.h:351 [inline]
       blkg_create+0x9f4/0x1158 block/blk-cgroup.c:320
       blkcg_init_disk+0xd0/0x318 block/blk-cgroup.c:1259
       __alloc_disk_node+0x26c/0x484 block/genhd.c:1412
       __blk_alloc_disk+0x40/0xbc block/genhd.c:1451
       brd_alloc+0x324/0x610 drivers/block/brd.c:424
       brd_init+0x134/0x1a8 drivers/block/brd.c:529
       do_one_initcall+0x260/0xacc init/main.c:1298
       do_initcall_level+0x154/0x214 init/main.c:1371
       do_initcalls+0x58/0xac init/main.c:1387
       do_basic_setup+0x8c/0xa0 init/main.c:1406
       kernel_init_freeable+0x3a4/0x528 init/main.c:1626
       kernel_init+0x24/0x29c init/main.c:1514
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:864

-> #1 (&q->queue_lock){..-.}-{2:2}:
       __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
       _raw_spin_lock_irq+0x70/0x9c kernel/locking/spinlock.c:170
       spin_lock_irq include/linux/spinlock.h:376 [inline]
       throtl_pending_timer_fn+0x104/0xdcc block/blk-throttle.c:1200
       call_timer_fn+0x1c0/0xa1c kernel/time/timer.c:1504
       expire_timers kernel/time/timer.c:1549 [inline]
       __run_timers+0x554/0x718 kernel/time/timer.c:1820
       run_timer_softirq+0x7c/0x114 kernel/time/timer.c:1833
       handle_softirqs+0x318/0xd58 kernel/softirq.c:571
       __do_softirq+0x14/0x20 kernel/softirq.c:605
       ____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:80
       call_on_irq_stack+0x24/0x4c arch/arm64/kernel/entry.S:893
       do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:85
       invoke_softirq kernel/softirq.c:452 [inline]
       __irq_exit_rcu+0x264/0x4d4 kernel/softirq.c:654
       irq_exit_rcu+0x14/0x84 kernel/softirq.c:666
       __el1_irq arch/arm64/kernel/entry-common.c:472 [inline]
       el1_interrupt+0x38/0x68 arch/arm64/kernel/entry-common.c:486
       el1h_64_irq_handler+0x18/0x24 arch/arm64/kernel/entry-common.c:491
       el1h_64_irq+0x64/0x68 arch/arm64/kernel/entry.S:581
       arch_counter_get_cntvct+0x4/0x30 drivers/clocksource/arm_arch_timer.c:209
       __const_udelay arch/arm64/lib/delay.c:55 [inline]
       __udelay+0x60/0x70 arch/arm64/lib/delay.c:61
       try_check_zero+0x3b4/0x3e4 kernel/rcu/srcutree.c:975
       srcu_advance_state kernel/rcu/srcutree.c:1549 [inline]
       process_srcu+0x168/0x10e0 kernel/rcu/srcutree.c:1651
       process_one_work+0x7ac/0x1404 kernel/workqueue.c:2292
       worker_thread+0x8e4/0xfec kernel/workqueue.c:2439
       kthread+0x250/0x2d8 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:864

-> #0 ((&sq->pending_timer)){+.-.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x3338/0x7680 kernel/locking/lockdep.c:5049
       lock_acquire+0x26c/0x7cc kernel/locking/lockdep.c:5662
       timer_delete_sync+0x9c/0x210 kernel/time/timer.c:1448
       del_timer_sync include/linux/timer.h:198 [inline]
       throtl_pd_free+0x20/0x48 block/blk-throttle.c:493
       blkcg_deactivate_policy+0x2cc/0x4a8 block/blk-cgroup.c:1497
       blk_throtl_exit+0x9c/0x13c block/blk-throttle.c:2415
       blkcg_init_disk+0x2a4/0x318 block/blk-cgroup.c:1283
       __alloc_disk_node+0x26c/0x484 block/genhd.c:1412
       __blk_mq_alloc_disk+0x114/0x1e4 block/blk-mq.c:4146
       nbd_dev_add+0x314/0x938 drivers/block/nbd.c:1812
       nbd_genl_connect+0x8fc/0x17f4 drivers/block/nbd.c:1995
       genl_family_rcv_msg_doit net/netlink/genetlink.c:756 [inline]
       genl_family_rcv_msg net/netlink/genetlink.c:833 [inline]
       genl_rcv_msg+0x948/0xc2c net/netlink/genetlink.c:850
       netlink_rcv_skb+0x20c/0x3b8 net/netlink/af_netlink.c:2493
       genl_rcv+0x38/0x50 net/netlink/genetlink.c:861
       netlink_unicast_kernel net/netlink/af_netlink.c:1311 [inline]
       netlink_unicast+0x65c/0x898 net/netlink/af_netlink.c:1337
       netlink_sendmsg+0x834/0xb18 net/netlink/af_netlink.c:1859
       sock_sendmsg_nosec net/socket.c:718 [inline]
       __sock_sendmsg net/socket.c:730 [inline]
       ____sys_sendmsg+0x55c/0x848 net/socket.c:2519
       ___sys_sendmsg net/socket.c:2573 [inline]
       __sys_sendmsg+0x26c/0x33c net/socket.c:2602
       __do_sys_sendmsg net/socket.c:2611 [inline]
       __se_sys_sendmsg net/socket.c:2609 [inline]
       __arm64_sys_sendmsg+0x80/0x94 net/socket.c:2609
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

Chain exists of:
  (&sq->pending_timer) --> &q->queue_lock --> &blkcg->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&blkcg->lock);
                               lock(&q->queue_lock);
                               lock(&blkcg->lock);
  lock((&sq->pending_timer));

 *** DEADLOCK ***

4 locks held by syz-executor958/4311:
 #0: ffff80001811f250 (cb_lock){++++}-{3:3}, at: genl_rcv+0x28/0x50 net/netlink/genetlink.c:860
 #1: ffff80001811f108 (genl_mutex){+.+.}-{3:3}, at: genl_lock net/netlink/genetlink.c:33 [inline]
 #1: ffff80001811f108 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0x114/0xc2c net/netlink/genetlink.c:848
 #2: ffff0000ceafdc10 (&q->queue_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
 #2: ffff0000ceafdc10 (&q->queue_lock){..-.}-{2:2}, at: blkcg_deactivate_policy+0xf4/0x4a8 block/blk-cgroup.c:1486
 #3: ffff80001ce537b0 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #3: ffff80001ce537b0 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ac/0x4a8 block/blk-cgroup.c:1493

stack backtrace:
CPU: 0 PID: 4311 Comm: syz-executor958 Not tainted 6.1.123-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2048
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x3338/0x7680 kernel/locking/lockdep.c:5049
 lock_acquire+0x26c/0x7cc kernel/locking/lockdep.c:5662
 timer_delete_sync+0x9c/0x210 kernel/time/timer.c:1448
 del_timer_sync include/linux/timer.h:198 [inline]
 throtl_pd_free+0x20/0x48 block/blk-throttle.c:493
 blkcg_deactivate_policy+0x2cc/0x4a8 block/blk-cgroup.c:1497
 blk_throtl_exit+0x9c/0x13c block/blk-throttle.c:2415
 blkcg_init_disk+0x2a4/0x318 block/blk-cgroup.c:1283
 __alloc_disk_node+0x26c/0x484 block/genhd.c:1412
 __blk_mq_alloc_disk+0x114/0x1e4 block/blk-mq.c:4146
 nbd_dev_add+0x314/0x938 drivers/block/nbd.c:1812
 nbd_genl_connect+0x8fc/0x17f4 drivers/block/nbd.c:1995
 genl_family_rcv_msg_doit net/netlink/genetlink.c:756 [inline]
 genl_family_rcv_msg net/netlink/genetlink.c:833 [inline]
 genl_rcv_msg+0x948/0xc2c net/netlink/genetlink.c:850
 netlink_rcv_skb+0x20c/0x3b8 net/netlink/af_netlink.c:2493
 genl_rcv+0x38/0x50 net/netlink/genetlink.c:861
 netlink_unicast_kernel net/netlink/af_netlink.c:1311 [inline]
 netlink_unicast+0x65c/0x898 net/netlink/af_netlink.c:1337
 netlink_sendmsg+0x834/0xb18 net/netlink/af_netlink.c:1859
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg net/socket.c:730 [inline]
 ____sys_sendmsg+0x55c/0x848 net/socket.c:2519
 ___sys_sendmsg net/socket.c:2573 [inline]
 __sys_sendmsg+0x26c/0x33c net/socket.c:2602
 __do_sys_sendmsg net/socket.c:2611 [inline]
 __se_sys_sendmsg net/socket.c:2609 [inline]
 __arm64_sys_sendmsg+0x80/0x94 net/socket.c:2609
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
nbd: failed to add new device