linux-kernel - Re: [PATCH v2] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops

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Message-ID: <Z346WcFfn6jTckm8@gpd3>
Date: Wed, 8 Jan 2025 09:42:01 +0100
From: Andrea Righi <arighi@...dia.com>
To: Changwoo Min <changwoo@...lia.com>
Cc: tj@...nel.org, void@...ifault.com, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in
 scx_ops_bypass()

On Wed, Jan 08, 2025 at 05:33:07PM +0900, Changwoo Min wrote:
> scx_ops_bypass() iterates all CPUs to re-enqueue all the scx tasks.
> For each CPU, it acquires a lock using rq_lock() regardless of whether
> a CPU is offline or the CPU is currently running a task in a higher
> scheduler class (e.g., deadline). The rq_lock() is supposed to be used
> for online CPUs, and the use of rq_lock() may trigger an unnecessary
> warning in rq_pin_lock(). Therefore, replace rq_lock() to
> raw_spin_rq_lock() in scx_ops_bypass().
> 
> This change fixes: 0e7ffff1b811 ("scx: Fix raciness in scx_ops_bypass()")

We should use the `Fixes:` tag, put this right before your SoB line:

 Fixes: 0e7ffff1b811 ("scx: Fix raciness in scx_ops_bypass()")

> 
> Without this change, we observe the following warnings:

Maybe report only the first warning, or even something small like this
should be sufficient to identify the issue I think:

 [    6.615205] rq->balance_callback && rq->balance_callback != &balance_push_callback
 [    6.615208] WARNING: CPU: 2 PID: 0 at kernel/sched/sched.h:1730 __schedule+0x1130/0x1c90

Thanks,
-Andrea