======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc6-syzkaller-00291-g3db61221f4e8 #0 Not tainted
------------------------------------------------------
syz-executor.2/13005 is trying to acquire lock:
ffff8880493be0a8 ((&sq->pending_timer)){+.-.}-{0:0}, at: del_timer_sync+0xd0/0x2a0 kernel/time/timer.c:1417

but task is already holding lock:
ffffffff91809d50 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
ffffffff91809d50 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ab/0x540 block/blk-cgroup.c:1519

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&blkcg->lock){....}-{2:2}:
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5666
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:154
       spin_lock include/linux/spinlock.h:349 [inline]
       blkg_create+0x949/0x10a0 block/blk-cgroup.c:344
       blkcg_init_queue+0xb9/0x300 block/blk-cgroup.c:1285
       __alloc_disk_node+0x2ce/0x590 block/genhd.c:1367
       __blk_alloc_disk+0x2c/0x80 block/genhd.c:1406
       brd_alloc+0x315/0x720 drivers/block/brd.c:391
       brd_init+0x102/0x1c6 drivers/block/brd.c:477
       do_one_initcall+0x1b9/0x3e0 init/main.c:1296
       do_initcall_level+0x168/0x218 init/main.c:1369
       do_initcalls+0x4b/0x8c init/main.c:1385
       kernel_init_freeable+0x3f1/0x57b init/main.c:1623
       kernel_init+0x19/0x2b0 init/main.c:1512
       ret_from_fork+0x1f/0x30

-> #1 (&q->queue_lock){..-.}-{2:2}:
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5666
       __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
       _raw_spin_lock_irq+0xae/0xf0 kernel/locking/spinlock.c:170
       spin_lock_irq include/linux/spinlock.h:374 [inline]
       throtl_pending_timer_fn+0xe9/0xfb0 block/blk-throttle.c:1152
       call_timer_fn+0xf5/0x210 kernel/time/timer.c:1474
       expire_timers kernel/time/timer.c:1519 [inline]
       __run_timers+0x772/0x980 kernel/time/timer.c:1790
       run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1803
       __do_softirq+0x362/0x773 kernel/softirq.c:571
       __irq_exit_rcu+0xcf/0x150 kernel/softirq.c:650
       irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
       sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1106
       asm_sysvec_apic_timer_interrupt+0x16/0x20
       rcu_dynticks_curr_cpu_in_eqs include/linux/context_tracking.h:121 [inline]
       rcu_is_watching+0x18/0xb0 kernel/rcu/tree.c:718
       rcu_read_unlock include/linux/rcupdate.h:735 [inline]
       batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:412 [inline]
       batadv_nc_worker+0x1c4/0x5b0 net/batman-adv/network-coding.c:719
       process_one_work+0x877/0xdb0 kernel/workqueue.c:2289
       worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
       kthread+0x266/0x300 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30

-> #0 ((&sq->pending_timer)){+.-.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain+0x1873/0x6c00 kernel/locking/lockdep.c:3829
       __lock_acquire+0x1292/0x1f60 kernel/locking/lockdep.c:5053
       lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5666
       del_timer_sync+0xec/0x2a0 kernel/time/timer.c:1417
       throtl_pd_free+0x15/0x40 block/blk-throttle.c:500
       blkcg_deactivate_policy+0x328/0x540 block/blk-cgroup.c:1523
       blk_throtl_exit+0x86/0x120 block/blk-throttle.c:2337
       blkcg_init_queue+0x281/0x300 block/blk-cgroup.c:1304
       __alloc_disk_node+0x2ce/0x590 block/genhd.c:1367
       __blk_mq_alloc_disk+0x11b/0x1e0 block/blk-mq.c:3942
       loop_add+0x325/0x9b0 drivers/block/loop.c:1983
       loop_control_ioctl+0x108/0x770 drivers/block/loop.c:2155
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

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 ***

2 locks held by syz-executor.2/13005:
 #0: ffff888020f200d0 (&q->queue_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline]
 #0: ffff888020f200d0 (&q->queue_lock){..-.}-{2:2}, at: blkcg_deactivate_policy+0xe3/0x540 block/blk-cgroup.c:1512
 #1: ffffffff91809d50 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
 #1: ffffffff91809d50 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ab/0x540 block/blk-cgroup.c:1519

stack backtrace:
CPU: 1 PID: 13005 Comm: syz-executor.2 Not tainted 6.0.0-rc6-syzkaller-00291-g3db61221f4e8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
 check_noncircular+0x2cc/0x390 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain+0x1873/0x6c00 kernel/locking/lockdep.c:3829
 __lock_acquire+0x1292/0x1f60 kernel/locking/lockdep.c:5053
 lock_acquire+0x182/0x3c0 kernel/locking/lockdep.c:5666
 del_timer_sync+0xec/0x2a0 kernel/time/timer.c:1417
 throtl_pd_free+0x15/0x40 block/blk-throttle.c:500
 blkcg_deactivate_policy+0x328/0x540 block/blk-cgroup.c:1523
 blk_throtl_exit+0x86/0x120 block/blk-throttle.c:2337
 blkcg_init_queue+0x281/0x300 block/blk-cgroup.c:1304
 __alloc_disk_node+0x2ce/0x590 block/genhd.c:1367
 __blk_mq_alloc_disk+0x11b/0x1e0 block/blk-mq.c:3942
 loop_add+0x325/0x9b0 drivers/block/loop.c:1983
 loop_control_ioctl+0x108/0x770 drivers/block/loop.c:2155
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f62edc8a669
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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f62eee14168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f62eddabf80 RCX: 00007f62edc8a669
RDX: 0000000020000040 RSI: 0000000000004c80 RDI: 0000000000000003
RBP: 00007f62eee141d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007ffe4adb555f R14: 00007f62eee14300 R15: 0000000000022000
 </TASK>