[dpdk-dev] [PATCH] vhost: fix double read of descriptor flags

[Ilya Maximets]

Flags could be updated in a separate process leading to the
inconsistent check.

Additionally, read marked as 'volatile' to highlight the shared
nature of the variable and avoid such issues in the future.

Fixes: d3211c98c456 ("vhost: add helpers for packed virtqueues")
Cc: ***@dpdk.org

Signed-off-by: Ilya Maximets <***@samsung.com>
---
lib/librte_vhost/vhost.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 5218f1b12..84cbee2b6 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -393,8 +393,10 @@ vq_is_packed(struct virtio_net *dev)
static inline bool
desc_is_avail(struct vring_packed_desc *desc, bool wrap_counter)
{
- return wrap_counter == !!(desc->flags & VRING_DESC_F_AVAIL) &&
- wrap_counter != !!(desc->flags & VRING_DESC_F_USED);
+ uint16_t flags = *((volatile uint16_t *) &desc->flags);
+
+ return wrap_counter == !!(flags & VRING_DESC_F_AVAIL) &&
+ wrap_counter != !!(flags & VRING_DESC_F_USED);
}

#define VHOST_LOG_PAGE 4096