Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932401AbaGNTIg (ORCPT ); Mon, 14 Jul 2014 15:08:36 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:59525 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752518AbaGNTI1 (ORCPT ); Mon, 14 Jul 2014 15:08:27 -0400 Message-ID: <53C42AA8.8010107@codeaurora.org> Date: Mon, 14 Jul 2014 12:08:24 -0700 From: Saravana Kannan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Viresh Kumar CC: "Rafael J . Wysocki" , Todd Poynor , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , "linux-arm-msm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Stephen Boyd Subject: Re: [PATCH v2] cpufreq: Don't destroy/realloc policy/sysfs on hotplug/suspend References: <1404959850-11617-1-git-send-email-skannan@codeaurora.org> <1405052287-4744-1-git-send-email-skannan@codeaurora.org> <2f549e6e4871ccf2a94dd4c8872c7a0b.squirrel@www.codeaurora.org> <53C0A12A.2060204@codeaurora.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/13/2014 11:09 PM, Viresh Kumar wrote: > On 12 July 2014 08:14, Saravana Kannan wrote: > >>>> I'm just always adding the real nodes to the first CPU in a cluster >>>> independent of which CPU gets added first. Makes it easier to know which >>>> ones to symlink. See comment next to policy->cpu for full context. >>> >>> >>> Yeah, and that is the order in which CPUs will boot and cpufreq_add_dev() >>> will be called. So, isn't policy->cpu the right CPU always? >> >> >> No, the "first" cpu in a cluster doesn't need to be the first one to be >> added. An example is 2x2 cluster system where the system is booted with max >> cpus = 2 and then cpu3 could be onlined first by userspace. > > Because we are getting rid of much of the complexity now, I do not want > policy->cpu to keep changing. Just fix it up to the cpu for which the policy > gets created first. That's it. No more changes required. It doesn't matter at > userspace which cpu owns it as symlinks would anyway duplicate it under > every cpu. I think you missed one my of comments in the email. I agree with what you are saying here. I'll just do it as a separate patch to keep this one simpler. I don't want to touch all the governors and other potential uses of policy->cpu in this patch. >> Yeah, it is pretty convolution. But pretty much anywhere in the gov code >> where policy->cpu is used could cause this. The specific crash I hit was in >> this code: >> >> static void od_dbs_timer(struct work_struct *work) >> { >> struct od_cpu_dbs_info_s *dbs_info = >> container_of(work, struct od_cpu_dbs_info_s, >> cdbs.work.work); >> unsigned int cpu = dbs_info->cdbs.cur_policy->cpu; >> >> ======= CPU is policy->cpu here. >> >> struct od_cpu_dbs_info_s *core_dbs_info = &per_cpu(od_cpu_dbs_info, >> cpu); >> >> ======= Picks the per CPU struct of an offline CPU >> >> >> >> mutex_lock(&core_dbs_info->cdbs.timer_mutex); >> >> ======= Dies trying to lock a destroyed mutex > > I am still not getting it. Why would we get into this if policy->cpu is fixed > once at boot ? > Yeah, it definitely crashes if policy->cpu if an offline cpu. Because the mutex would be uninitialized if it's stopped after boot or it would never have been initialized (depending on how you fix policy->cpu at boot). Look at this snippet on the actual tree and it should be pretty evident. -Saravana -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/