On Mon, 25 Apr 2005, Andrew Morton wrote: > I have vague memories of this being discussed at some length last year. > Nothing comprehensive came of it, except that perhaps the kdump code should > spin with irqs off for a couple of seconds so the DMA and IRQs stop.
Like Pavel said, this won't work. > (Ongoing DMA is not a problem actually, because the kdump kernel won't be > using that memory anyway) For PCI devices at least, DMA _can_ be disabled in a uniform way as devices are discovered. Some platforms might not want to do this for fear it would kill the initial console display. IRQs _cannot_ be disabled in a uniform way. So they remain a problem. > For kdump we really don't want to be doing fancy driver shutdown inside a > crashed kernel. It would be better to just jump to the new kernel and > to reset the hardware from there. DMA doesn't matter, and maybe IRQs can > be handled with a sustained local_irq_disable() (hard). But at some point you have to enable local IRQs, and then you're in trouble if a device without a driver is generating requests. Unless the new kernel can run with interrupts entirely disabled? Seems pretty unlikely. The real problem is that, in general, hardware _can't_ be reset properly by a new kernel. There are things that can help, like the PCI USB quirks code. That might be enough to handle the most pressing existing problems; certainly it would avoid the USB issues we've seen. (But it needs to be updated to avoid interfering with normal operations during resume-from-disk.) Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
