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 PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Sun, 09 Nov 2014 09:12:42 -0500 From: Prarit Bhargava <prarit@...hat.com> To: "Rafael J. Wysocki" <rjw@...ysocki.net> CC: linux-kernel@...r.kernel.org, robert.schoene@...dresden.de, sboyd@...eaurora.org, Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org Subject: Re: [PATCH 5/5] cpufreq, add BUG() messages in critical paths to aid debugging failures On 11/08/2014 04:46 PM, Rafael J. Wysocki wrote: > On Saturday, November 08, 2014 08:33:35 AM Prarit Bhargava wrote: >> >> On 11/07/2014 09:00 PM, Rafael J. Wysocki wrote: >>> On Wednesday, November 05, 2014 09:53:59 AM Prarit Bhargava wrote: >>>> Add some additional debug to capture failures in the locking scheme for >>>> cpufreq. Instead of just a NULL pointer, these warnings will capture failure >>>> points if the locking scheme for cpufreq is broken. >>>> >>>> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net> >>>> Cc: Viresh Kumar <viresh.kumar@...aro.org> >>>> Cc: linux-pm@...r.kernel.org >>>> Signed-off-by: Prarit Bhargava <prarit@...hat.com> >>>> --- >>>> drivers/cpufreq/cpufreq_governor.c | 32 +++++++++++++++++++++++++++----- >>>> 1 file changed, 27 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c >>>> index b1ee597..f158882 100644 >>>> --- a/drivers/cpufreq/cpufreq_governor.c >>>> +++ b/drivers/cpufreq/cpufreq_governor.c >>>> @@ -161,9 +161,18 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) >>>> EXPORT_SYMBOL_GPL(dbs_check_cpu); >>>> >>>> static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data, >>>> - unsigned int delay) >>>> + unsigned int delay, >>>> + struct cpufreq_policy *policy) >>>> { >>>> - struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); >>>> + struct cpu_dbs_common_info *cdbs; >>>> + >>>> + if (!dbs_data->cdata) { >>>> + pr_emerg("common_dbs_data is NULL for %s but initialized = %d", >>>> + policy->governor->name, >>>> + atomic_read(&policy->governor->initialized)); >>>> + BUG(); >>> >>> Is it necessary to crash the kernel here? >> >> Yes. dbs_data->cdata is referenced right below. >> >>> >>>> + } >>>> + cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); >> >> and we'll NULL pointer panic right here without any of the debug info above :( > > Can we possibly avoid the panic? > > Adding BUG() instead of a NULL pointer deref is not much improvement. (sorry for the lowercase typing. i fractured my elbow and have resorted to single hand typing ....) rafael, i understand your concern and my description is clearly lacking for this patch. this patch is not meant to be a fix but is meant to capture debug info for future issues in this code. i thought about only doing the pr_emerg() but that results in situations where other threads may continue processing and i lose state in crashdump :(. bug() is a good idea here imo. P. > >> >>>> >>>> mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay); >>>> } >>>> @@ -185,10 +194,11 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy, >>>> * those works are canceled during CPU_DOWN_PREPARE so they >>>> * can't possibly run on any other CPU. >>>> */ >>>> - __gov_queue_work(raw_smp_processor_id(), dbs_data, delay); >>>> + __gov_queue_work(raw_smp_processor_id(), dbs_data, delay, >>>> + policy); >>>> } else { >>>> for_each_cpu(i, policy->cpus) >>>> - __gov_queue_work(i, dbs_data, delay); >>>> + __gov_queue_work(i, dbs_data, delay, policy); >>>> } >>>> >>>> out_unlock: >>>> @@ -258,7 +268,13 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, >>>> else >>>> dbs_data = cdata->gdbs_data; >>>> >>>> - 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(); >>> >>> And here? >>> >> >> Ditto -- dbs_data is dereferenced in the call path and will NULL pointer panic. >> >> P. >> >>>> + } >>>> >>>> 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) { >>>> + pr_emerg("Removing governor %s but initialized = %d, dbs_data->usage_count = 0\n", >>>> + policy->governor->name, >>>> + atomic_read(&policy->governor->initialized)); >>>> + BUG(); >>>> + } >>>> sysfs_remove_group(get_governor_parent_kobj(policy), >>>> get_sysfs_attr(dbs_data)); >>>> >>>> >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-pm" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/
Powered by blists - more mailing lists