linux-kernel - Re: [PATCH v3] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops

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Message-ID: <Z36skl9hpe1O6ubU@slm.duckdns.org>
Date: Wed, 8 Jan 2025 06:49:22 -1000
From: Tejun Heo <tj@...nel.org>
To: Changwoo Min <changwoo@...lia.com>
Cc: void@...ifault.com, arighi@...dia.com, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in
 scx_ops_bypass()

On Thu, Jan 09, 2025 at 12:08:06AM +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().
> 
> Without this change, we observe the following warning:
> 
> ===== START =====
> [    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
> =====  END  =====
> 
> Fixes: 0e7ffff1b811 ("scx: Fix raciness in scx_ops_bypass()")
> Signed-off-by: Changwoo Min <changwoo@...lia.com>

Applied to sched_ext/for-6.13-fixes.

Thanks.

-- 
tejun