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From: Peter Zijlstra on 26 Mar 2010 03:00 On Fri, 2010-03-26 at 03:18 +0000, Jamie Lokier wrote: > Peter Zijlstra wrote: > > On Tue, 2010-03-16 at 13:21 +1100, Nick Piggin wrote: > > > > > > > > > Agreed (btw. Peter is there any way to turn lock debugging back on? > > > it's annoying when cpufreq hotplug code or something early breaks and > > > you have to reboot in order to do any testing). > > > > Not really, the only way to do that is to get the full system back into > > a known (zero) lock state and then fully reset the lockdep state. > > How about: Set a variable nr_pending = number of CPUs, run a task on > each CPU which disables interrupts, atomically decrements nr_pending > and then spins waiting for it to become negative (raw, not counted in > lockdep), and whichever one takes it to zero, that task knows there > are no locks held, and can reset the lockdep state. Then sets it to > -1 to wake everyone. Nope, won't work, you can easily preempt a lock holder. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Jamie Lokier on 26 Mar 2010 08:00
Peter Zijlstra wrote: > On Fri, 2010-03-26 at 03:18 +0000, Jamie Lokier wrote: > > Peter Zijlstra wrote: > > > On Tue, 2010-03-16 at 13:21 +1100, Nick Piggin wrote: > > > > > > > > > > > > Agreed (btw. Peter is there any way to turn lock debugging back on? > > > > it's annoying when cpufreq hotplug code or something early breaks and > > > > you have to reboot in order to do any testing). > > > > > > Not really, the only way to do that is to get the full system back into > > > a known (zero) lock state and then fully reset the lockdep state. > > > > How about: Set a variable nr_pending = number of CPUs, run a task on > > each CPU which disables interrupts, atomically decrements nr_pending > > and then spins waiting for it to become negative (raw, not counted in > > lockdep), and whichever one takes it to zero, that task knows there > > are no locks held, and can reset the lockdep state. Then sets it to > > -1 to wake everyone. > > Nope, won't work, you can easily preempt a lock holder. Doh, yes of course. I promise to get some sleep before further appearances :-) -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |