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virtio: Decrement avail idx on buffer detach 

When detaching a buffer from a vq, the avail.idx value should be
decremented as well.

This was noticed by hot-unplugging a virtio console port and then
plugging in a new one on the same number (re-using the vqs which were
just 'disowned').  qemu reported

   'Guest moved used index from 0 to 256'

when any IO was attempted on the new port.

CC: stable@kernel.org
Reported-by: juzhang <juzhang@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Amit Shah 2011-03-16 19:12:10 +05:30 committed by Rusty Russell
parent 584f790467
commit b3258ff1d6
1 changed files with 1 additions and 0 deletions
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1
drivers/virtio/virtio_ring.c
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@ -371,6 +371,7 @@ void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
/* detach_buf clears data, so grab it now. */
buf = vq->data[i];
detach_buf(vq, i);
vq->vring.avail->idx--;
END_USE(vq);
return buf;
}