On Thu, 2012-01-12 at 15:37 +0000, Mel Gorman wrote: > On Thu, Jan 12, 2012 at 04:18:12PM +0100, Peter Zijlstra wrote: > > On Wed, 2012-01-11 at 10:11 +0000, Mel Gorman wrote: > > > At least one bug report has > > > been seen on ppc64 against a 3.0 era kernel that looked like a bug > > > receiving interrupts on a CPU being offlined. > > > > Got details on that Mel? The preempt_disable() in on_each_cpu() should > > serialize against the stop_machine() crap in unplug. > > I might have added 2 and 2 together and got 5. > > The stack trace clearly was while sending IPIs in on_each_cpu() and > always when under memory pressure and stuck in direct reclaim. This was > on !PREEMPT kernels where preempt_disable() is a no-op. That is why I > thought get_online_cpu() would be necessary. For non-preempt the required scheduling of stop_machine() will have to wait even longer. Still there might be something funny, some of the hotplug notifiers are ran before the stop_machine thing does its thing so there might be some fun interaction. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href