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On Sun, 27 Aug 2006 11:41:55 +0530 Dipankar Sarma <dipankar@in.ibm.com> wrote: > Now coming to the read-side of lock_cpu_hotplug() - cpu hotplug > is a very special asynchronous event. You cannot protect against > it using your own subsystem lock because you don't control > access to cpu_online_map. Yes you do. Please, read _cpu_up(), _cpu_down() and the example in workqueue_cpu_callback(). It's really very simple. > With multiple low-level subsystems > needing it, it also becomes difficult to work out the lock > hierarchies. That'll matter if we do crappy code. Let's not do that? > > > > I rather doubt that anyone will be hitting the races in practice. I'd > > recommend simply removing all the lock_cpu_hotplug() calls for 2.6.18. > > I don't think that is a good idea. The code's already racy and I don't think anyone has reported a cpufreq-vs-hotplug race. > 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). It needs to be ripped out and some understanding, thought and design should be applied to the problem. > People > seem to have just got lazy with lock_cpu_hotplug(). That's because lock_cpu_hotplug() purports to be some magical thing which makes all your troubles go away. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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