linux-sg2042/drivers/vhost
Michael S. Tsirkin 0d4993563b vhost: fix barrier pairing
According to memory-barriers.txt, an smp memory barrier in guest
should always be paired with an smp memory barrier in host,
and I quote "a lack of appropriate pairing is almost certainly an
error". In case of vhost, failure to flush out used index
update before looking at the interrupt disable flag
could result in missed interrupts, resulting in
networking hang under stress.

This might happen when flags read bypasses used index write.
So we see interrupts disabled and do not interrupt, at the
same time guest writes flags value to enable interrupt,
reads an old used index value, thinks that
used ring is empty and waits for interrupt.

Note: the barrier we pair with here is in
drivers/virtio/virtio_ring.c, function
vring_enable_cb.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
2010-05-12 18:04:04 +03:00
..
Kconfig net/macvtap: add vhost support 2010-02-18 14:08:38 -08:00
Makefile vhost_net: a kernel-level virtio server 2010-01-15 01:43:29 -08:00
net.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
vhost.c vhost: fix barrier pairing 2010-05-12 18:04:04 +03:00
vhost.h vhost_net: a kernel-level virtio server 2010-01-15 01:43:29 -08:00