linux-kernel - Re: [PATCH 5/5] cpufreq, add BUG() messages in critical paths to aid debugging failures

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 11 Nov 2014 18:41:21 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Robert Schöne <robert.schoene@...dresden.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 5/5] cpufreq, add BUG() messages in critical paths to aid
 debugging failures

On 11 November 2014 17:48, Prarit Bhargava <prarit@...hat.com> wrote:
> the problem is tht the userful information is the values of initialized,
> enabled, and what the  event was :(
>
> in every case i ended up needing the values.

So, just add a pr_debug instead and let every thing crash as it does today.

>>> @@ -258,7 +268,13 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
>>> -       WARN_ON(!dbs_data && (event != CPUFREQ_GOV_POLICY_INIT));
>>> +       if (!dbs_data && (event != CPUFREQ_GOV_POLICY_INIT)) {
>>> +               pr_emerg("governor_data is NULL but governor %s is initialized = %d [governor_enabled = %d event = %u]\n",
>>> +                        policy->governor->name,
>>> +                        atomic_read(&policy->governor->initialized),
>>> +                        policy->governor_enabled, event);
>>> +               BUG();
>>
>> How is the BUG better than the WARN here ?
>>
>
> we null pointer panic later on, and again the useful values are the ones displayed.

For the values, I would add a pr_debug() for all cases. And maybe just
do s/WARN_ON/BUG_ON

>>>         switch (event) {
>>>         case CPUFREQ_GOV_POLICY_INIT:
>>> @@ -329,6 +345,12 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
>>>         case CPUFREQ_GOV_POLICY_EXIT:
>>>                 mutex_lock(&dbs_data->usage_count_mutex);
>>>                 if (atomic_dec_and_test(&dbs_data->usage_count)) {
>>> +                       if (atomic_read(&policy->governor->initialized) > 1) {
>>
>> Isn't this wrong? Consider 4 CPUs with separate clock line and have set
>> governor-per-policy to true. EXIT will be called for every CPU hotplug and
>> initialized will be 4 initially..
>>
>> Or I am still vacation lag'd ? :)
>
> oh, is that right?  i'll look into that.

What is right? sorry couldn't understand :(
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/