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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c6114c845984 Linux 6.1.65
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1323ad54e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=90a251dce2a1f6a2
dashboard link: https://syzkaller.appspot.com/bug?extid=bf9ed1d36bc87fe3d0fb
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1663ab72e80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16d23422e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/81de3f46fb80/disk-c6114c84.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/67e2306cffb3/vmlinux-c6114c84.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7007e58d973b/Image-c6114c84.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bf9ed1...@syzkaller.appspotmail.com

do_el0_svc+0x64/0x218 arch/arm64/kernel/syscall.c:206
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
6.1.65-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor383/4225 is trying to acquire lock:
ffff0000dd8f70a8 ((&sq->pending_timer)){+.-.}-{0:0}, at: del_timer_sync+0x74/0x210 kernel/time/timer.c:1417

but task is already holding lock:
ffff800019a62cb0 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:350 [inline]
ffff800019a62cb0 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ac/0x4a8 block/blk-cgroup.c:1476

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:350 [inline]
blkg_create+0x9f4/0x1158 block/blk-cgroup.c:320
blkcg_init_disk+0xd0/0x318 block/blk-cgroup.c:1242
__alloc_disk_node+0x26c/0x484 block/genhd.c:1413
__blk_alloc_disk+0x40/0xbc block/genhd.c:1452
brd_alloc+0x2ac/0x5c8 drivers/block/brd.c:397
brd_init+0x108/0x1c4 drivers/block/brd.c:484
do_one_initcall+0x260/0xacc init/main.c:1296
do_initcall_level+0x154/0x214 init/main.c:1369
do_initcalls+0x58/0xac init/main.c:1385
do_basic_setup+0x8c/0xa0 init/main.c:1404
kernel_init_freeable+0x3a4/0x528 init/main.c:1624
kernel_init+0x24/0x29c init/main.c:1512
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:375 [inline]
throtl_pending_timer_fn+0x104/0xdcc block/blk-throttle.c:1200
call_timer_fn+0x1c0/0xa1c kernel/time/timer.c:1474
expire_timers kernel/time/timer.c:1519 [inline]
__run_timers+0x554/0x718 kernel/time/timer.c:1790
run_timer_softirq+0x7c/0x114 kernel/time/timer.c:1803
__do_softirq+0x314/0xe38 kernel/softirq.c:571
____do_softirq+0x14/0x20 arch/arm64/kernel/irq.c:79
call_on_irq_stack+0x24/0x4c arch/arm64/kernel/entry.S:893
do_softirq_own_stack+0x20/0x2c arch/arm64/kernel/irq.c:84
invoke_softirq kernel/softirq.c:452 [inline]
__irq_exit_rcu+0x264/0x4d4 kernel/softirq.c:650
irq_exit_rcu+0x14/0x84 kernel/softirq.c:662
__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_local_irq_restore arch/arm64/include/asm/irqflags.h:122 [inline]
lock_acquire+0x2ac/0x7cc kernel/locking/lockdep.c:5665
__might_fault+0xc4/0x124 mm/memory.c:5811
_copy_from_user include/linux/uaccess.h:124 [inline]
copy_from_user include/linux/uaccess.h:161 [inline]
get_timespec64+0xa0/0x2d0 kernel/time/time.c:787
__do_sys_clock_nanosleep kernel/time/posix-timers.c:1297 [inline]
__se_sys_clock_nanosleep kernel/time/posix-timers.c:1285 [inline]
__arm64_sys_clock_nanosleep+0x1e4/0x38c kernel/time/posix-timers.c:1285
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x64/0x218 arch/arm64/kernel/syscall.c:206
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

-> #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
del_timer_sync+0x9c/0x210 kernel/time/timer.c:1417
throtl_pd_free+0x20/0x48 block/blk-throttle.c:493
blkcg_deactivate_policy+0x2cc/0x4a8 block/blk-cgroup.c:1480
blk_throtl_exit+0x9c/0x13c block/blk-throttle.c:2413
blkcg_init_disk+0x2a4/0x318 block/blk-cgroup.c:1266
__alloc_disk_node+0x26c/0x484 block/genhd.c:1413
__blk_mq_alloc_disk+0x114/0x1e4 block/blk-mq.c:4100
loop_add+0x2c4/0x8c8 drivers/block/loop.c:2001
loop_control_ioctl+0xec/0x650 drivers/block/loop.c:2173
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x64/0x218 arch/arm64/kernel/syscall.c:206
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 ***

2 locks held by syz-executor383/4225:
#0: ffff0000d54880d0 (&q->queue_lock){..-.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:375 [inline]
#0: ffff0000d54880d0 (&q->queue_lock){..-.}-{2:2}, at: blkcg_deactivate_policy+0xf4/0x4a8 block/blk-cgroup.c:1469
#1: ffff800019a62cb0 (&blkcg->lock){....}-{2:2}, at: spin_lock include/linux/spinlock.h:350 [inline]
#1: ffff800019a62cb0 (&blkcg->lock){....}-{2:2}, at: blkcg_deactivate_policy+0x1ac/0x4a8 block/blk-cgroup.c:1476

stack backtrace:
CPU: 1 PID: 4225 Comm: syz-executor383 Not tainted 6.1.65-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
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
del_timer_sync+0x9c/0x210 kernel/time/timer.c:1417
throtl_pd_free+0x20/0x48 block/blk-throttle.c:493
blkcg_deactivate_policy+0x2cc/0x4a8 block/blk-cgroup.c:1480
blk_throtl_exit+0x9c/0x13c block/blk-throttle.c:2413
blkcg_init_disk+0x2a4/0x318 block/blk-cgroup.c:1266
__alloc_disk_node+0x26c/0x484 block/genhd.c:1413
__blk_mq_alloc_disk+0x114/0x1e4 block/blk-mq.c:4100
loop_add+0x2c4/0x8c8 drivers/block/loop.c:2001
loop_control_ioctl+0xec/0x650 drivers/block/loop.c:2173
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x64/0x218 arch/arm64/kernel/syscall.c:206
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


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