linux-kernel - Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

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Message-ID: <1917362.abr2Y4p7vh@vostro.rjw.lan>
Date:	Thu, 31 Jul 2014 20:38:22 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Saravana Kannan <skannan@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lenny Szubowicz <lszubowi@...hat.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

On Thursday, July 31, 2014 01:57:29 PM Prarit Bhargava wrote:
> 
> On 07/31/2014 12:36 PM, Rafael J. Wysocki wrote:
> > On Thursday, July 31, 2014 06:23:18 AM Prarit Bhargava wrote:
> >>
> >> On 07/30/2014 10:16 PM, Rafael J. Wysocki wrote:
> >>> On Wednesday, July 30, 2014 06:36:00 PM Saravana Kannan wrote:
> >>>> On 07/30/2014 02:40 PM, Rafael J. Wysocki wrote:
> >>>>> On Wednesday, July 30, 2014 10:18:25 AM Prarit Bhargava wrote:
> >>>>>>
> >>>>>> On 07/29/2014 08:03 PM, Rafael J. Wysocki wrote:
> >>>>>>> On Tuesday, July 29, 2014 07:46:02 AM Prarit Bhargava wrote:
> >>>>>
> >>>>> [cut]
> >>>>>
> >>>>>>>> This patch effectively reverts commit 955ef483.
> >>>>
> >>>> The issue reported in this patch is valid. We are seeing that internally 
> >>>> too. I believe I reported it in another thread (within the past month).
> >>>>
> >>>> However, the original patch fixes a real deadlock issue (I'm too tired 
> >>>> to look it up now). We can revet the original, but it's going to bring 
> >>>> back the original issue. I just want to make sure Prarit and Raphael 
> >>>> realize this before proceeding.
> >>>>
> >>>> I do have plans for a proper fix for the mainline (not stable branches), 
> >>>> but plan to do that after the current set of suspend/hotplug patches go 
> >>>> through. The fix would be easier to make after that.
> >>>>
> >>>>>>>
> >>>>>>> OK, I'm convinced by this.
> >>>>>>>
> >>>>>>> I suppose we should push it for -stable from 3.10 through 3.15.x, right?
> >>>>>>
> >>>>>> Rafael, I think that is a good idea.  I'm not sure what the protocol is for
> >>>>>> adding stable@...nel.org though ...
> >>
> >> Rafael, let me (again) re-write the patch description.  I think Saravana has
> >> raised an important issue that I have not clearly identified why it is safe to
> >> remove this code in my patch description.  Also, I want to clearly identify the
> >> appropriate -stable releases to push this out to.
> >>
> >> I'll submit a [v3] later today or tomorrow.
> > 
> > In any case that's too late for 3.16 final, unless there's an -rc8.
> > 
> > Thanks for doing that work!
> 
> Ugh ... I tried this (yet another) large system and hit another panic :(.
> 
> I'm investigating now, and I'm hoping this is just something "new".

Well, I've applied your patch as is and I can push it to Linus.

However, if you want to update the changelog, I'll not do that, but in that
case the patch will have to wait for the next week.

Rafael

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