| Message ID | 53E158C1.6010701@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 08/05/2014 03:20 PM, Prarit Bhargava wrote: > > > On 08/05/2014 06:06 PM, Saravana Kannan wrote: >> On 08/05/2014 03:53 AM, Viresh Kumar wrote: >>> On 5 August 2014 16:17, Prarit Bhargava <prarit@redhat.com> wrote: >>>> Nope, not a stupid question. After reproducing (finally!) yesterday I've been >>>> wondering the same thing. >>> >>> Good to know that :) >>> >>>> I've been looking into *exactly* this. On any platform where >>>> cpu_weight(affected_cpus) == 1 for a particular cpu this lockdep trace should >>>> happen. >>> >>>> That's what I'm wondering too. I'm going to instrument the code to find out >>>> this morning. I'm wondering if this comes down to a lockdep class issue >>>> (perhaps lockdep puts globally defined locks like cpufreq_global_kobject in a >>>> different class?). >>> >>> Maybe, I tried this Hack to make this somewhat similar to the other case >>> on my platform with just two CPUs: >>> >>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >>> index 6f02485..6b4abac 100644 >>> --- a/drivers/cpufreq/cpufreq.c >>> +++ b/drivers/cpufreq/cpufreq.c >>> @@ -98,7 +98,7 @@ static DEFINE_MUTEX(cpufreq_governor_mutex); >>> >>> bool have_governor_per_policy(void) >>> { >>> - return !!(cpufreq_driver->flags & CPUFREQ_HAVE_GOVERNOR_PER_POLICY); >>> + return !(cpufreq_driver->flags & CPUFREQ_HAVE_GOVERNOR_PER_POLICY); >>> } >>> EXPORT_SYMBOL_GPL(have_governor_per_policy); >>> >>> >>> This should result in something similar to setting that per-policy-governor >>> flag (Actually I could have done that too :)), and I couldn't see that crash :( >>> >>> That needs more investigation now, probably we can get some champ of >>> sysfs stuff like Tejun/Greg into discussion now.. >> >> Stephen and I looked into this. This is not a sysfs framework difference. The >> reason we don't have this issue when we use global tunables is because we add >> the attribute group to the cpufreq_global_kobject and that kobject doesn't have >> a kobj_type ops similar to the per policy kobject. So, read/write to those >> attributes do NOT go through the generic show/store ops that wrap every other >> cpufreq framework attribute read/writes. >> >> So, none of those read/write do any kind of locking. They don't race with >> POLICY_EXIT (because we remove the sysfs group first thing in POLICY_EXIT) but >> might still race with START/STOPs (not sure, haven't looked closely yet). >> >> For example, writing to sampling_rate of ondemand governor might cause a race in >> update_sampling_rate(). It could race and happen between a STOP and POLICY_EXIT >> (triggered by hotplug, gov change, etc). >> >> So, this might be a completely separate bug that needs fixing when we don't use >> per policy govs. > > Yeah, the show_one & store_one macros don't have any locking in them :/. > > Okay ... at least that isn't the issue. I spent 1/2 the day trying to figure > out why > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index fa11a7d..6297c76 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -745,12 +745,14 @@ static struct attribute *default_attrs[] = { > #define to_policy(k) container_of(k, struct cpufreq_policy, kobj) > #define to_attr(a) container_of(a, struct freq_attr, attr) > > +/* PRARIT - in the CPUFREQ_HAVE_GOVERNOR_PER_POLICY, this is used */ > static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf) > { > struct cpufreq_policy *policy = to_policy(kobj); > struct freq_attr *fattr = to_attr(attr); > ssize_t ret; > > + printk("%s: kobject %p\n", __FUNCTION__, kobj); > if (!down_read_trylock(&cpufreq_rwsem)) > return -EINVAL; > > wasn't printing the kobject line when acpi-cpufreq didn't have the > CPUFREQ_HAVE_GOVERNOR_PER_POLICY flag. And I agree ... it is a bug. > Wait, should I stop reporting bugs so that my patch series gets reviewed? :P -Saravana
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index fa11a7d..6297c76 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -745,12 +745,14 @@ static struct attribute *default_attrs[] = { #define to_policy(k) container_of(k, struct cpufreq_policy, kobj) #define to_attr(a) container_of(a, struct freq_attr, attr) +/* PRARIT - in the CPUFREQ_HAVE_GOVERNOR_PER_POLICY, this is used */ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf) { struct cpufreq_policy *policy = to_policy(kobj); struct freq_attr *fattr = to_attr(attr); ssize_t ret; + printk("%s: kobject %p\n", __FUNCTION__, kobj); if (!down_read_trylock(&cpufreq_rwsem)) return -EINVAL;