Messages in this thread | | | Date | Sun, 27 Aug 2006 00:57:07 -0700 | From | Andrew Morton <> | Subject | Re: [RFC][PATCH 0/4] Redesign cpu_hotplug locking. |
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On Sun, 27 Aug 2006 13:07:30 +0530 Dipankar Sarma <dipankar@in.ibm.com> wrote:
> On Sat, Aug 26, 2006 at 11:46:18PM -0700, Andrew Morton wrote: > > On Sun, 27 Aug 2006 11:41:55 +0530 > > > > > The right thing to do would be to > > > do an audit and clean up the bad lock_cpu_hotplug() calls. > > > > No, that won't fix it. For example, take a look at all the *callers* of > > cpufreq_update_policy(). AFAICT they're all buggy. Fiddling with the > > existing lock_cpu_hotplug() sites won't fix that. (Possibly this > > particular problem can be fixed by checking that the relevant CPU is still > > online after the appropriate locking has been taken - dunno). > > > > This is a different issue from the ones that relates to lock_cpu_hotplug().
Well not really. The thinking goes "gee, we need to lock against CPU hotplug. THe CPU hotplug guys gave us lock_cpu_hotplug() so we're supposed to use that somethere". We see the result.
> This one seems like a cpufreq internal locking problem. > > On a quick look at this,
Me too. But fixing this will require a long look. What per-cpu resources are being used? How should they be locked? Implement.
> it seems to me that cpufreq_cpu_get() should > do exactly what you said - use a spinlock in each cpufreq_cpu_data[] to > protect the per-cpu flag and in cpufreq_cpu_get() check if > !data and data->online == 0. They may have to do - > > static struct cpufreq_data { > spinlock_t lock; > int flag; > struct cpufreq_policy *policy; > } cpufreq_cpu_data[NR_CPUS]; >
I think we're agreeing... cpufreq locking is busted, needs to be redone and, I would suggest, fancifying lock_cpu_hotplug() isn't the way to do it.
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