[dpdk-dev] [PATCH] vhost: fix external mbuf creation

yang_y_yi yang_y_yi at 163.com
Fri Oct 9 10:47:12 CEST 2020


Tested-by: Yi Yang <yangyi01 at inspur.com>





















At 2020-10-07 20:53:18, "Olivier Matz" <olivier.matz at 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: stable at dpdk.org
>
>Signed-off-by: Olivier Matz <olivier.matz at 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_yi@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


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