linux-kernel - Re: [PATCH v2] sched_ext: initialize built-in idle state before ops.init()

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Message-ID: <Z-RoWbLDwgqGYvtq@slm.duckdns.org>
Date: Wed, 26 Mar 2025 10:49:29 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: initialize built-in idle state before
 ops.init()

On Tue, Mar 25, 2025 at 10:32:12AM +0100, Andrea Righi wrote:
> A BPF scheduler may want to use the built-in idle cpumasks in ops.init()
> before the scheduler is fully initialized, either directly or through a
> BPF timer for example.
> 
> However, this would result in an error, since the idle state has not
> been properly initialized yet.
> 
> This can be easily verified by modifying scx_simple to call
> scx_bpf_get_idle_cpumask() in ops.init():
> 
> $ sudo scx_simple
> 
> DEBUG DUMP
> ===========================================================================
> 
> scx_simple[121] triggered exit kind 1024:
>   runtime error (built-in idle tracking is disabled)
> ...
> 
> Fix this by properly initializing the idle state before ops.init() is
> called. With this change applied:
> 
> $ sudo scx_simple
> local=2 global=0
> local=19 global=11
> local=23 global=11
> ...
> 
> Fixes: d73249f88743d ("sched_ext: idle: Make idle static keys private")
> Signed-off-by: Andrea Righi <arighi@...dia.com>

Applied to sched_ext/for-6.15-fixes.

Thanks.

-- 
tejun