linux-kernel - Re: RE: [EXT] Re: [PATCH net v2] octeontx2-pf: Fix page pool cache index corruption.

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Message-ID: <20230907101527.45YwOJcG@linutronix.de>
Date:   Thu, 7 Sep 2023 12:15:27 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Ratheesh Kannoth <rkannoth@...vell.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Geethasowjanya Akula <gakula@...vell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        Hariprasad Kelam <hkelam@...vell.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "alexander.duyck@...il.com" <alexander.duyck@...il.com>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        "linyunsheng@...wei.com" <linyunsheng@...wei.com>
Subject: Re: RE: [EXT] Re: [PATCH net v2] octeontx2-pf: Fix page pool cache
 index corruption.

On 2023-09-07 08:15:58 [+0000], Ratheesh Kannoth wrote:
> > From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > Subject: [EXT] Re: [PATCH net v2] octeontx2-pf: Fix page pool cache index
> > corruption.
> > >  	cq->refill_task_sched = false;
> > > +
> > > +	local_bh_disable();
> > > +	napi_schedule(wrk->napi);
> > > +	local_bh_enable();
> > 
> > This is a nitpick since I haven't look how it works exactly: Is it possible that the
> > wrk->napi pointer gets overwritten by
> > otx2_napi_handler() since you cleared cq->refill_task_sched() earlier?
> I don’t see any issue here.  As NAPI and workqueue execution is serialized (as interrupt is disabled when 
> Workqueue is scheduled).  I don’t think we can move "refill_task_sched = false" after local_bh_enable(). 
> But we can move refill_task_sched = false as below . but I don’t see a need. 

Right, there might be no issue I was just asking. I don't know how the
cq <-> NAPI mapping is working. If you say that there is no race/issue,
okay ;)

>  +
>  +	local_bh_disable();
>  +	napi_schedule(wrk->napi);
>   +	cq->refill_task_sched = false;
>  +	local_bh_enable();

Sebastian