linux-kernel - Re: [PATCH] sched_ext: idle: Handle migration-disabled tasks in idle selection

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Message-ID: <aHk-7UvELcnx8-wO@slm.duckdns.org>
Date: Thu, 17 Jul 2025 08:20:29 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	sched-ext@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched_ext: idle: Handle migration-disabled tasks in idle
 selection

On Sat, Jul 05, 2025 at 07:43:51AM +0200, Andrea Righi wrote:
> When SCX_OPS_ENQ_MIGRATION_DISABLED is enabled, migration-disabled tasks
> are also routed to ops.enqueue(). A scheduler may attempt to dispatch
> such tasks directly to an idle CPU using the default idle selection
> policy via scx_bpf_select_cpu_and() or scx_bpf_select_cpu_dfl().
> 
> This scenario must be properly handled by the built-in idle policy to
> avoid returning an idle CPU where the target task isn't allowed to run.
> Otherwise, it can lead to errors such as:
> 
>  EXIT: runtime error (SCX_DSQ_LOCAL[_ON] cannot move migration disabled Chrome_ChildIOT[291646] from CPU 3 to 14)
> 
> Prevent this by explicitly handling migration-disabled tasks in the
> built-in idle selection logic, maintaining their CPU affinity.
> 
> Fixes: a730e3f7a48bc ("sched_ext: idle: Consolidate default idle CPU selection kfuncs")
> Signed-off-by: Andrea Righi <arighi@...dia.com>

Applied to sched_ext/for-6.16-fixes.

Thanks.

-- 
tejun