linux-kernel - Re: [PATCH v2] sched_ext: Replace hardcoding with macro and minor typo fix

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Message-ID: <20241114173418.GA4643@maniforge>
Date: Thu, 14 Nov 2024 11:34:18 -0600
From: David Vernet <void@...ifault.com>
To: Tejun Heo <tj@...nel.org>
Cc: Zhao Mengmeng <zhaomzhao@....com>, zhaomengmeng@...inos.cn,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: Replace hardcoding with macro and minor
 typo fix

On Thu, Nov 14, 2024 at 07:12:31AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Wed, Nov 13, 2024 at 10:59:08AM +0800, Zhao Mengmeng wrote:
> > From: Zhao Mengmeng <zhaomengmeng@...inos.cn>
> > 
> > 1. replace hardcoding with SCX_KF_UNLOCKED.
> > 2. scx_next_task_picked() has been replaced with siwtch_class().
> > 3. minor typo fixes.
> > 
> > Signed-off-by: Zhao Mengmeng <zhaomengmeng@...inos.cn>
> > ---
> >  kernel/sched/ext.c             | 6 +++---
> >  tools/sched_ext/scx_qmap.bpf.c | 2 +-
> >  2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> > index 1b1c33f12dd7..832f77d1d318 100644
> > --- a/kernel/sched/ext.c
> > +++ b/kernel/sched/ext.c
> > @@ -2759,10 +2759,10 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
> >  		 * If the previous sched_class for the current CPU was not SCX,
> >  		 * notify the BPF scheduler that it again has control of the
> >  		 * core. This callback complements ->cpu_release(), which is
> > -		 * emitted in scx_next_task_picked().
> > +		 * emitted in switch_class().
> >  		 */
> >  		if (SCX_HAS_OP(cpu_acquire))
> > -			SCX_CALL_OP(0, cpu_acquire, cpu_of(rq), NULL);
> > +			SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_acquire, cpu_of(rq), NULL);
> 
> I think this is actually a bug. David, shouldn't this be SCX_KF_REST?

Yes, good catch. We're holding the rq lock so SCX_KF_UNLOCKED isn't safe. I
agree this should be SCX_KF_REST.

Thanks,
David

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