On Mon, Mar 02, 2015 at 12:31:06PM +0100, Cornelia Huck wrote: > On Mon, 2 Mar 2015 12:13:58 +0100 > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > On Mon, Mar 02, 2015 at 10:37:26AM +1030, Rusty Russell wrote: > > > Thomas Huth <thuth@xxxxxxxxxxxxxxxxxx> writes: > > > > On Thu, 26 Feb 2015 11:50:42 +1030 > > > > Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: > > > > > > > >> Thomas Huth <thuth@xxxxxxxxxxxxxxxxxx> writes: > > > >> > Hi all, > > > >> > > > > >> > with the recent kernel 3.19, I get a kernel warning when I start my > > > >> > KVM guest on s390 with virtio balloon enabled: > > > >> > > > >> The deeper problem is that virtio_ccw_get_config just silently fails on > > > >> OOM. > > > >> > > > >> Neither get_config nor set_config are expected to fail. > > > > > > > > AFAIK this is currently not a problem. According to > > > > http://lwn.net/Articles/627419/ these kmalloc calls never > > > > fail because they allocate less than a page. > > > > > > I strongly suggest you unlearn that fact. > > > The fix for this is in two parts: > > > > > > 1) Annotate using sched_annotate_sleep() and add a comment: we may spin > > > a few times in low memory situations, but this isn't a high > > > performance path. > > > > > > 2) Handle get_config (and other) failure in some more elegant way. > > Do you mean we need to enable the caller to deal with get_config > failures (and the transport to relay those failures)? I agree with that. We can certainly tweak code to bypass need to kmalloc on get_config. Why is it doing these allocs? What's wrong with using vcdev->config directly? > > > > > > Cheers, > > > Rusty. > > > > I agree, but I'd like to point out that even without kmalloc, > > on s390 get_config is blocking - it's waiting > > for a hardware interrupt. > > > > And it makes sense: config is not data path, I don't think > > we should spin there. > > > > So I think besides these two parts, we still need my two patches: > > virtio-balloon: do not call blocking ops when !TASK_RUNNING > > virtio_console: avoid config access from irq > > in 4.0. > > > > agree? > > I agree that we need those fixes as well. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
