On Wed, 25 Apr 2007, Christoph Lameter wrote: > On Wed, 25 Apr 2007, Hugh Dickins wrote: > > > > Right. local_irq_save does not switch off preemption as I thought. > > > > Strange comment. Preemption is not possible while IRQs are disabled, > > but new_slab() rightly reenables them within itself in the __GFP_WAIT > > case, since it's going off to do a page allocation and may need to wait. > > Yes I expected local_irq_save to increase the preempt count and then > local_irq_enable to simply enable interrupts without affecting the preempt > count. Thus the process should stay on the same processor. > > Never thought it would be possible to move to a different processor in mid > flight.
But, surely you wouldn't have expected it to stay on the processor throughout the waiting page allocation?? I think you're misremembering your expectations, and this was just a simple, understandable, oversight. Quite a serious one, though: it got caught in my case by the NULL dereference, but it's probably been switching cpu there much more often - one cpu diddling with what's private to another, with unpredictable results. Hugh - 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/