Thanks Oliver for posting this patch, it clearly explain his concern, I totally
agree this change. I tested it by OVS DPDK, it works well.
At 2020-10-07 20:53:18, "Olivier Matz" <olivier.m...@6wind.com> wrote:
>In virtio_dev_extbuf_alloc(), the shinfo structure used to store
>the reference counter and the free callback of the external buffer
>is by default stored inside the mbuf data.
>
>This is wrong because the mbuf (and its data) can be freed before
>the external buffer, for instance in the following situation:
>
> pkt2 = rte_pktmbuf_alloc(mp);
> rte_pktmbuf_attach(pkt2, pkt);
> rte_pktmbuf_free(pkt);
>
>After this, pkt is freed, but it still contains shinfo, which is
>referenced by pkt2.
>
>Fix this by always storing the shinfo beside the external buffer.
>
>Fixes: c3ff0ac70acb ("vhost: improve performance by supporting large buffer")
>Cc: sta...@dpdk.org
>
>Signed-off-by: Olivier Matz <olivier.m...@6wind.com>
>---
>
>Hi,
>
>I found this issue by code review while discussing about this
>patchset [1]. I did not tested the patch, but as I'm only removing
>one path among the two, I don't expect that it breaks anything.
>
>[1] http://inbox.dpdk.org/dev/20200730120900.108232-1-yang_y...@163.com/
>
>Regards,
>Olivier
>
> lib/librte_vhost/virtio_net.c | 30 ++++++++----------------------
> 1 file changed, 8 insertions(+), 22 deletions(-)
>
>diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
>index 0a0bea1a5a..008f5ceb04 100644
>--- a/lib/librte_vhost/virtio_net.c
>+++ b/lib/librte_vhost/virtio_net.c
>@@ -2098,16 +2098,8 @@ virtio_dev_extbuf_alloc(struct rte_mbuf *pkt, uint32_t
>size)
> rte_iova_t iova;
> void *buf;
>
>- /* Try to use pkt buffer to store shinfo to reduce the amount of memory
>- * required, otherwise store shinfo in the new buffer.
>- */
>- if (rte_pktmbuf_tailroom(pkt) >= sizeof(*shinfo))
>- shinfo = rte_pktmbuf_mtod(pkt,
>- struct rte_mbuf_ext_shared_info *);
>- else {
>- total_len += sizeof(*shinfo) + sizeof(uintptr_t);
>- total_len = RTE_ALIGN_CEIL(total_len, sizeof(uintptr_t));
>- }
>+ total_len += sizeof(*shinfo) + sizeof(uintptr_t);
>+ total_len = RTE_ALIGN_CEIL(total_len, sizeof(uintptr_t));
>
> if (unlikely(total_len > UINT16_MAX))
> return -ENOSPC;
>@@ -2118,18 +2110,12 @@ virtio_dev_extbuf_alloc(struct rte_mbuf *pkt, uint32_t
>size)
> return -ENOMEM;
>
> /* Initialize shinfo */
>- if (shinfo) {
>- shinfo->free_cb = virtio_dev_extbuf_free;
>- shinfo->fcb_opaque = buf;
>- rte_mbuf_ext_refcnt_set(shinfo, 1);
>- } else {
>- shinfo = rte_pktmbuf_ext_shinfo_init_helper(buf, &buf_len,
>- virtio_dev_extbuf_free, buf);
>- if (unlikely(shinfo == NULL)) {
>- rte_free(buf);
>- VHOST_LOG_DATA(ERR, "Failed to init shinfo\n");
>- return -1;
>- }
>+ shinfo = rte_pktmbuf_ext_shinfo_init_helper(buf, &buf_len,
>+ virtio_dev_extbuf_free, buf);
>+ if (unlikely(shinfo == NULL)) {
>+ rte_free(buf);
>+ VHOST_LOG_DATA(ERR, "Failed to init shinfo\n");
>+ return -1;
> }
>
> iova = rte_malloc_virt2iova(buf);
>--
>2.25.1
