[Devel] [PATCH vz10] cgroup: fix css_set_lock IRQ unsafe usage in check_freeze_timeout()

[Pavel Tikhomirov]

Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

On 3/17/26 15:08, Vasileios Almpanis wrote:
> lockdep reports an inconsistent lock state involving css_set_lock,
> triggered via cgroup_events_show() -> check_freeze_timeout():
> 
>   WARNING: inconsistent lock state
>   inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
> 
>   Possible unsafe locking scenario:
> 
>         CPU0
>         ----
>    lock(css_set_lock);
>    <Interrupt>
>      lock(css_set_lock);
> 
>    *** DEADLOCK ***
> 
> The lock is currently taken with spin_lock()  in check_freeze_timeout(),
> which does not disable interrupts. However, css_set_lock is also
> acquired from IRQ/softirq context in RCU callbacks during task
> teardown, making it unsafe to take the lock with interrupts enabled.
> 
> This can lead to a deadlock if an interrupt fires while holding
> css_set_lock and attempts to re-acquire it.
> 
> Fix this by switching to spin_lock_irq() semantics via
> scoped_guard(spinlock_irq, ...), ensuring interrupts are disabled
> while holding css_set_lock in this path.
> 
> This matches the locking requirements of css_set_lock.
> 
> Fixes: 3cc887c3d0faa ("cgroup-v2/freezer: Print information about unfreezable process")
> https://virtuozzo.atlassian.net/browse/VSTOR-127046
> 
> Signed-off-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>
> 
> Feature: cgroup/freeze: enhance logging
> ---
>  kernel/cgroup/cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 040e7e36c238..376c9bbd1c41 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -4296,7 +4296,7 @@ static void check_freeze_timeout(struct cgroup *cgrp)
>  	u64 freeze_jiffies;
>  	int timeout;
>  
> -	scoped_guard(spinlock, &css_set_lock) {
> +	scoped_guard(spinlock_irq, &css_set_lock) {
>  		if (!test_bit(CGRP_FREEZE, &cgrp->flags) ||
>  		    test_bit(CGRP_FROZEN, &cgrp->flags))
>  			return;

-- 
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.