Re: [PATCH 01/12] sched/core: Avoid false migration warning for proxy donors

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The warning for migrating a migration-disabled task is incorrectly suppressed for all sleeping tasks when proxy execution is enabled, instead of just for blocked proxy donors.
--

--- Patch [1]: [PATCH 01/12] sched/core: Avoid false migration warning for proxy donors ---
commit 3b0fd432ea71e1ba27a8e56bb387fb372b053daf
Author: Andrea Righi <[email protected]>

sched/core: Avoid false migration warning for proxy donors

This commit updates set_task_cpu to suppress a false positive warning when
migrating a proxy donor. It allows moving a blocked scheduling context to
another CPU even when the donor task has migration disabled.

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
[ ... ]
> @@ -3376,7 +3376,13 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>  	 */
>  	WARN_ON_ONCE(!cpu_online(new_cpu));
>  
> -	WARN_ON_ONCE(is_migration_disabled(p));
> +	/*
> +	 * Proxy execution can move a blocked task's scheduling context to any
> +	 * CPU without moving its migration-disabled execution context. The
> +	 * wakeup path will return the task to a CPU where it can execute.
> +	 */
> +	WARN_ON_ONCE(is_migration_disabled(p) &&
> +		     !(sched_proxy_exec() && p->is_blocked));

[Severity: Medium]
Does this logic inadvertently suppress the warning for all sleeping tasks
rather than just proxy donors?

Because p->is_blocked is set unconditionally for all sleeping tasks when
__schedule calls try_to_block_task, this condition in set_task_cpu appears
to suppress the warning for any migration-disabled sleeping task whenever
proxy execution is globally enabled.

If another scheduler component, such as a load balancer or a BPF sched_ext
extension, incorrectly migrates a normal sleeping task that has migration
disabled, this overly broad check might hide the invalid migration and mask
further issues.

>  
>  	trace_sched_migrate_task(p, new_cpu);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1