From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
Stephen Warren <swarren@wwwdotorg.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
cpufreq <cpufreq@vger.kernel.org>
Subject: Re: cpufreq_stats NULL deref on second system suspend
Date: Thu, 12 Sep 2013 12:16:12 +0530 [thread overview]
Message-ID: <52316334.6080603@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAKohpo=LuoKTf+mX1oBt97K3sJVu0iN=whN7VGw6kuartnrr+w@mail.gmail.com>
On 09/12/2013 12:11 PM, Viresh Kumar wrote:
> On 12 September 2013 11:56, Srivatsa S. Bhat
> <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>> I had the same thought when solving this bug.. We have had similar issues with
>> CPU hotplug notifiers too: why are they invoked in the same order during both
>> CPU down and up, instead of reversing the order? I even had a patchset to perform
>> reverse-invocation of notifiers.. http://lwn.net/Articles/508072/
>> ... but people didn't find that very compelling to have.
>>
>
>> It does to me too, but I think the reason nobody really bothered is because perhaps
>> not many other subsystems care about the order in which CPUs are torn down or
>> brought up; they just need the total number to match.. cpufreq is one exception
>> as we saw with this bug.
>
> Probably its time to re-spin that series and make CPUFreq as one of the users
> of that patchset.. Resume should be just opposite of suspend and so
> that patchset
> would make sense even if not many people care about it :)
>
> Over that there is one more problem that I see, don't know if it is really a big
> issue..
>
> After a suspend/resume value of policy->cpu may get changed... And so the
> hierarchy of sysfs cpufreq files too.. Folder that had links to other
> CPUs folder
> can now be actual folders instead of links and vice versa..
>
> Don't know if this can break something ??
>
Interesting observation :-) But we just managed to retain sysfs file permissions
across suspend/resume with a lot of trouble and regressions. That's probably
good enough for some time to come ;-) We can retain folder/links when somebody
really finds a need to do that ;-)
Of course, if we change the suspend/resume sequence and that fixes this, that
would be like getting it for free, nobody would say no to it ;-)
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2013-09-12 6:50 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-09 19:22 cpufreq_stats NULL deref on second system suspend Stephen Warren
2013-09-09 20:01 ` Rafael J. Wysocki
2013-09-09 20:01 ` Stephen Warren
2013-09-09 20:24 ` Rafael J. Wysocki
2013-09-09 21:29 ` Stephen Warren
2013-09-09 23:14 ` Rafael J. Wysocki
2013-09-10 20:53 ` Stephen Warren
2013-09-10 22:34 ` Rafael J. Wysocki
2013-09-11 10:21 ` Srivatsa S. Bhat
2013-09-11 10:44 ` Viresh Kumar
2013-09-11 10:45 ` Viresh Kumar
2013-09-11 11:14 ` Srivatsa S. Bhat
2013-09-11 11:59 ` Viresh Kumar
2013-09-11 13:56 ` Srivatsa S. Bhat
2013-09-12 5:52 ` Viresh Kumar
2013-09-12 6:26 ` Srivatsa S. Bhat
2013-09-12 6:41 ` Viresh Kumar
2013-09-12 6:46 ` Srivatsa S. Bhat [this message]
2013-09-12 6:52 ` Viresh Kumar
2013-09-12 7:14 ` Srivatsa S. Bhat
2013-09-12 15:55 ` Stephen Warren
2013-09-12 17:26 ` Srivatsa S. Bhat
2013-09-13 4:26 ` Viresh Kumar
2013-09-11 11:10 ` Srivatsa S. Bhat
2013-09-11 11:15 ` Viresh Kumar
2013-09-11 11:17 ` Srivatsa S. Bhat
2013-09-11 11:41 ` Viresh Kumar
2013-09-11 11:09 ` Srivatsa S. Bhat
2013-09-11 16:05 ` Stephen Warren
2013-09-11 18:03 ` Srivatsa S. Bhat
2013-09-11 18:42 ` Srivatsa S. Bhat
2013-09-11 19:03 ` Stephen Warren
2013-09-11 19:46 ` Srivatsa S. Bhat
2013-09-11 20:07 ` Stephen Warren
2013-09-11 20:05 ` Srivatsa S. Bhat
2013-09-12 6:04 ` Viresh Kumar
2013-09-12 6:00 ` Viresh Kumar
2013-09-12 5:58 ` Viresh Kumar
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