From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753414AbaKHBGg (ORCPT ); Fri, 7 Nov 2014 20:06:36 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:55087 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752682AbaKHBGe (ORCPT ); Fri, 7 Nov 2014 20:06:34 -0500 From: "Rafael J. Wysocki" To: Geert Uytterhoeven Cc: Viresh Kumar , Thomas Petazzoni , Lucas Stach , linux-pm@vger.kernel.org, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] [RFC] cpufreq: Avoid crash in resume on SMP without OPP Date: Sat, 08 Nov 2014 02:27:22 +0100 Message-ID: <2837337.oz3KWfM6uC@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <1415117125-27069-1-git-send-email-geert+renesas@glider.be> References: <1415117125-27069-1-git-send-email-geert+renesas@glider.be> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday, November 04, 2014 05:05:25 PM Geert Uytterhoeven wrote: > When resuming from s2ram on an SMP system without cpufreq operating > points (e.g. there's no "operating-points" property for the CPU node in > DT, or the platform doesn't use DT yet), the kernel crashes when > bringing CPU 1 online: > > Enabling non-boot CPUs ... > CPU1: Booted secondary processor > Unable to handle kernel NULL pointer dereference at virtual address 0000003c > pgd = ee5e6b00 > [0000003c] *pgd=6e579003, *pmd=6e588003, *pte=00000000 > Internal error: Oops: a07 [#1] SMP ARM > Modules linked in: > CPU: 0 PID: 1246 Comm: s2ram Tainted: G W 3.18.0-rc3-koelsch-01614-g0377af242bb175c8-dirty #589 > task: eeec5240 ti: ee704000 task.ti: ee704000 > PC is at __cpufreq_add_dev.isra.24+0x24c/0x77c > LR is at __cpufreq_add_dev.isra.24+0x244/0x77c > pc : [] lr : [] psr: 60000153 > sp : ee705d48 ip : ee705d48 fp : ee705d84 > r10: c04e0450 r9 : 00000000 r8 : 00000001 > r7 : c05426a8 r6 : 00000001 r5 : 00000001 r4 : 00000000 > r3 : 00000000 r2 : 00000000 r1 : 20000153 r0 : c0542734 > > Verify that policy is not NULL before dereferencing it to fix this. > > Signed-off-by: Geert Uytterhoeven > --- > Notes: > - Is this the right fix? The fix looks correct to me. To my eyes what happens is that cpufreq_driver->init() in __cpufreq_add_dev() fails and then cpufreq_cpu_data_fallback is cleared. cpufreq_cpu_data is not set for the CPU, so cpufreq_cpu_data_fallback is NULL all the time. Then, during resume, __cpufreq_add_dev() is called again and it calls cpufreq_policy_restore(), because cpufreq_suspended is set. You know the rest. :-) I'm queuing this up for the next PM pull request (most likely next week for -rc5). > - Interestingly, the crash is the same as the one reported in > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c81407fe573d8ac3c7150f5373475598c59197de > ("cpufreq: cpufreq-dt: Restore default cpumask_setall(policy->cpus)"), > but the cause is different. > > - The crash was initially observed on sh73a0/kzm9g-legacy, but it can > easily be reproduced on e.g. r8a7791/koelsch, by removing the > "operating-points" property from the cpu0 node in > arch/arm/boot/dts/r8a7791.dtsi, or by any other means to make the > call to dev_pm_opp_init_cpufreq_table() in > drivers/cpufreq/cpufreq-dt.c:cpufreq_init() fail. > > - I did not add > > Fixes: 6e2c89d16d987e6e ("cpufreq: move call to __find_governor() to cpufreq_init_policy()") To me, that should be: Fixes: 8414809c6a1e (cpufreq: Preserve policy structure across suspend/resume) and therefore should go into 3.12+. I'll add the appropriate tags. > > as I couldn't verify that the issue is also present in that (old) > version (there have been too many s2ram-related platform and driver > fixes since v3.15). > --- > drivers/cpufreq/cpufreq.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 644b54e1e7d13e8e..4473eba1d6b0b608 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1022,7 +1022,8 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu) > > read_unlock_irqrestore(&cpufreq_driver_lock, flags); > > - policy->governor = NULL; > + if (policy) > + policy->governor = NULL; > > return policy; > } > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.