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SubjectRe: 2.6.35 Regression/oops from virtio: return ENOMEM on out of memory patch
On Mon, Jul 19, 2010 at 06:16:10PM +0300, Michael S. Tsirkin wrote:
> On Mon, Jul 19, 2010 at 11:02:16AM -0400, Chris Mason wrote:
> > Hi everyone,
> >
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=686d363786a53ed28ee875b84ef24e6d5126ef6f
> >
> > I've been having problems with my long running stress runs and tracked
> > it down to the above commit. Under load I get a couple of GFP_ATOMIC
> > allocation failures from virtio per day (not really surprising), and in
> > the past it would carry on happily.
> >
> > Now I get the atomic allocation failure followed by this:
> >
> > BUG: unable to handle kernel paging request at ffff88087c37e458
> > IP: [<ffffffff812e3752>] virtqueue_add_buf_gfp+0x305/0x353
> >
> > (Full oops below).
> >
> > Looking at virtqueue_add_buf_gfp, it does:
> >
> > /* If the host supports indirect descriptor tables, and we have multiple
> > * buffers, then go indirect. FIXME: tune this threshold */
> > if (vq->indirect && (out + in) > 1 && vq->num_free) {
> > head = vring_add_indirect(vq, sg, out, in, gfp);
> > if (head != vq->vring.num)
> > goto add_head;
> > }
> > [ ... ]
> >
> > add_head:
> > /* Set token. */
> > vq->data[head] = data;
> >
> > Since vring_add_indirect is returning -ENOMEM, head is -ENOMEM and things
> > go bad pretty quickly. Full oops below, afraid I don't know the virtio
> > code well enough to provide the clean and obvious fix (outside of
> > reverting) at this late rc.
>
> Good catch! Can you verify this fix please?
>
> virtio: fix oops on OOM
>
> virtio ring was changed to return an error code on OOM,
> but one caller was missed and still checks for vq->vring.num.
> The fix is just to check for <0 error code.
>
> Long term it might make sense to change goto add_head to
> just return an error on oom instead, but let's apply
> a minimal fix for 2.6.35.
>

Great, that looks sane, I'll give it a shot.

-chris


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