linux-kernel - Re: [PATCH v2 5/5] sched/fair: cleanup for SIS

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Message-ID: <20220907085133.nazbi7wftff46jrg@suse.de>
Date:   Wed, 7 Sep 2022 09:51:33 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Josh Don <joshdon@...gle.com>, Chen Yu <yu.c.chen@...el.com>,
        Yicong Yang <yangyicong@...wei.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] sched/fair: cleanup for SIS_PROP

On Wed, Sep 07, 2022 at 03:59:33PM +0800, Abel Wu wrote:
> On 9/1/22 10:03 PM, Mel Gorman wrote:
> > On Thu, Sep 01, 2022 at 09:11:07PM +0800, Abel Wu wrote:
> > > The sched-domain of this cpu is only used when SIS_PROP is enabled,
> > > and it should be irrelevant whether the local sd_llc is valid or
> > > not, since all we care about is target sd_llc if !SIS_PROP.
> > > 
> > > Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
> > 
> > This could conceivably result in an uninitialised memory access if
> > SIS_PROP was enabled while select_idle_cpu is running. I'm not sure if
> > it can happen when jump labels are in use but I think it could happen
> > for !CONFIG_JUMP_LABEL updating the sysctl_sched_features bitmap updated
> > via sysctl.
> > 
> > The patch is still a good idea because it moves an unlikely rcu_deference
> > out of the default path for sched features but either this_sd needs to
> > be initialised to NULL and checked or the this_sd lookup needs to happen
> > twice at a slight additional cost to the default-disabled SIS_PROP path.
> > 
> 
> Hi Mel, please check the following resent patch, Thanks!
> 
> https://lore.kernel.org/lkml/20220902033032.79846-5-wuyun.abel@bytedance.com/

Weird, I don't remember seeing this patch even though I'm cc'd on it. It
looks fine so even though it's the wrong thread;

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs