From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: cpufreq_stats NULL deref on second system suspend Date: Wed, 11 Sep 2013 14:07:12 -0600 Message-ID: <5230CD70.50202@wwwdotorg.org> References: <522E1FEF.6080803@wwwdotorg.org> <1775778.MeiRhuYy7o@vostro.rjw.lan> <522F86AD.6010603@wwwdotorg.org> <2521560.SfeNbV74nj@vostro.rjw.lan> <52304439.3030301@linux.vnet.ibm.com> <523094CD.3000506@wwwdotorg.org> <5230B078.3070306@linux.vnet.ibm.com> <5230B991.3040702@linux.vnet.ibm.com> <5230BE75.7040307@wwwdotorg.org> <5230C89D.7010801@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5230C89D.7010801@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: "Srivatsa S. Bhat" Cc: "Rafael J. Wysocki" , Viresh Kumar , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , cpufreq On 09/11/2013 01:46 PM, Srivatsa S. Bhat wrote: > On 09/12/2013 12:33 AM, Stephen Warren wrote: >> On 09/11/2013 12:42 PM, Srivatsa S. Bhat wrote: >> ... >>> OK, I took a second look at the code, and I suspect that applying the >>> second patch might help. So can you try by applying both the patches >>> please[1][2]? >>> >> ... >>> [1]. http://marc.info/?l=linux-kernel&m=137889516210816&w=2 >>> [2]. http://marc.info/?l=linux-kernel&m=137889800511940&w=2 >> >> Yes, with both of those patches applies, the problem is solved:-) >> >> I was going to test the second patch originally, but it sounded like it >> was more of a cleanup rather than a fix for my issue, so I didn't bother >> when I found the problem wasn't solved by patch 1. Sorry! >> > > Well, honestly, even I had intended the second patch as a cleanup and > hadn't asked you to test it ;-) Only when you reported that the first patch > failed to solve your problem, I realized that the second patch was > important too! :-) Thanks for testing! > >> For the record, I'm testing on a 2-CPU system, so I'm not sure whether >> your explanation applies; it talks about CPUs 2 and 3 whereas I only >> have CPUs 0 and 1, but perhaps your explanation applies equally to any >> pair of CPUs? >> > > Yes, it applies to any pair of CPUs, as long as the CPU first taken down > is not the policy->cpu. In your case, it applies like this: > IIUC, CPU0 is the boot cpu, and hence it wont be taken offline using hotplug. > So only CPU 1 is taken offline during suspend. And if it is not the policy->cpu, > then it hits the very same bug that I described with the analogy of CPUs 2 > and 3. > >> For the record, here's the information you requested in the other email: >> >> # cat /sys/devices/system/cpu/cpu*/cpufreq/related_cpus >> 0 1 >> 0 1 > > Thanks! It would have been more useful to somehow know which was the > policy->cpu. But looking at the problem, certainly CPU0 was the policy->cpu > in your case. Yes, I believe CPU0 since, > # ls -l /sys/devices/system/cpu/cpu1/cpufreq > lrwxrwxrwx 1 root root 0 Jan 1 00:01 /sys/devices/system/cpu/cpu1/cpufreq -> ../cpu0/cpufreq and cpu0/cpufreq/ has all the files in it. ... > So can you see if patch 1 + this above fix solves your problem as well? > Then we can retain the original patch 2 as a cleanup, after these 2 patches. > This organization also makes the code look better and understandable. Yes, both patch 1+3 and 1+3+2 work fine.