On Wed, 16 May 2007 16:40:59 -0700 (PDT) Christoph Lameter <[EMAIL PROTECTED]> wrote:
> On Wed, 16 May 2007, Andrew Morton wrote: > > > (I hope. Might have race windows in which the percpu_counter_sum() count is > > inaccurate?) > > The question is how do these race windows affect the locking scheme? The race to which I refer here is if another CPU is running percpu_counter_sum() in the window between the clearing of the bit in cpu_online_map and the CPU_DEAD callout. Maybe that's too small to care about in the short-term, dunno. Officially we should fix that by taking lock_cpu_hotplug() in percpu_counter_sum(), but I hate that thing. I was thinking of putting a cpumask into the counter. If we do that then there's no race at all: everything happens under fbc->lock. This would be a preferable fix, if we need to fix it. But I'd prefer that freezer-based cpu-hotplug comes along and saves us again. umm, actually, we can fix the race by using CPU_DOWN_PREPARE instead of CPU_DEAD. Because it's OK if percpu_counter_sum() looks at a gone-away CPU's slot. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
