[v6.1] possible deadlock in throtl_pending_timer_fn (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7dc732d24ff7 Linux 6.1.123
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1537b8b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=da1827eaa51b65c3
dashboard link: https://syzkaller.appspot.com/bug?extid=2dbae66a2b0fa90d2995
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b77a36eba7b4/disk-7dc732d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f5334562da28/vmlinux-7dc732d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f0a16f9a500c/Image-7dc732d2.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2dbae6...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.1.123-syzkaller #0 Not tainted
------------------------------------------------------
syz.0.189/5122 is trying to acquire lock:
ffff0000cf5d9040 (&q->queue_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
ffff0000cf5d9040 (&q->queue_lock){..-.}-{2:2}, at: throtl_pending_timer_fn+0x104/0xdcc block/blk-throttle.c:1200

but task is already holding lock:
ffff800008017c60 ((&sq->pending_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:41 [inline]
ffff800008017c60 ((&sq->pending_timer)){+.-.}-{0:0}, at: call_timer_fn+0xd0/0xa1c kernel/time/timer.c:1494

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((&sq->pending_timer)){+.-.}-{0:0}:
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_alloc_disk+0x40/0xbc block/genhd.c:1451
md_alloc+0x4e0/0xae8 drivers/md/md.c:5743
md_alloc_and_put drivers/md/md.c:5799 [inline]
md_probe+0x74/0xb0 drivers/md/md.c:5812
blk_request_module+0x184/0x1a8 block/genhd.c:752
blkdev_get_no_open+0x48/0xdc block/bdev.c:745
blkdev_get_by_dev+0x8c/0x8ec block/bdev.c:802
swsusp_check+0xf8/0x454 kernel/power/swap.c:1526
software_resume+0x130/0x680 kernel/power/hibernate.c:995
resume_store+0x108/0x1b0 kernel/power/hibernate.c:1200
kobj_attr_store+0x6c/0x90 lib/kobject.c:832
sysfs_kf_write+0x200/0x280 fs/sysfs/file.c:136
kernfs_fop_write_iter+0x334/0x48c fs/kernfs/file.c:334
call_write_iter include/linux/fs.h:2265 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x610/0x91c fs/read_write.c:584
ksys_write+0x15c/0x26c fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:646
__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

-> #1 (&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

-> #0 (&q->queue_lock){..-.}-{2:2}:
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
__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
el0_interrupt+0x80/0x260 arch/arm64/kernel/entry-common.c:717
__el0_irq_handler_common+0x18/0x24 arch/arm64/kernel/entry-common.c:724
el0t_64_irq_handler+0x10/0x1c arch/arm64/kernel/entry-common.c:729
el0t_64_irq+0x18c/0x190 arch/arm64/kernel/entry.S:586

other info that might help us debug this:

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

Possible unsafe locking scenario:

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

*** DEADLOCK ***

1 lock held by syz.0.189/5122:
#0: ffff800008017c60 ((&sq->pending_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:41 [inline]
#0: ffff800008017c60 ((&sq->pending_timer)){+.-.}-{0:0}, at: call_timer_fn+0xd0/0xa1c kernel/time/timer.c:1494

stack backtrace:
CPU: 1 PID: 5122 Comm: syz.0.189 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
__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
el0_interrupt+0x80/0x260 arch/arm64/kernel/entry-common.c:717
__el0_irq_handler_common+0x18/0x24 arch/arm64/kernel/entry-common.c:724
el0t_64_irq_handler+0x10/0x1c arch/arm64/kernel/entry-common.c:729
el0t_64_irq+0x18c/0x190 arch/arm64/kernel/entry.S:586
vkms_vblank_simulate: vblank timer overrun


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.