On Tue, Dec 21, 2021 at 9:32 AM Loftus, Ciara [off-list ref] wrote:

quoted

On Mon, Dec 20, 2021 at 9:10 PM Ciara Loftus [off-list ref]
wrote:

quoted

This commit initialises the xskb's free_list_node when the xskb is
allocated. This prevents a potential false negative returned from a call
to list_empty for that node, such as the one introduced in commit
199d983bc015 ("xsk: Fix crash on double free in buffer pool")

In my environment this issue caused packets to not be received by
the xdpsock application if the traffic was running prior to application
launch. This happened when the first batch of packets failed the xskmap
lookup and XDP_PASS was returned from the bpf program. This action is
handled in the i40e zc driver (and others) by allocating an skbuff,
freeing the xdp_buff and adding the associated xskb to the
xsk_buff_pool's free_list if it hadn't been added already. Without this
fix, the xskb is not added to the free_list because the check to determine
if it was added already returns an invalid positive result. Later, this
caused allocation errors in the driver and the failure to receive packets.

Thank you for this fix Ciara! Though I do think the Fixes tag should
be the one above: 199d983bc015 ("xsk: Fix crash on double free in
buffer pool"). Before that commit, there was no test for an empty list
in the xp_free path. The entry was unconditionally put on the list and
"initialized" in that way, so that code will work without this patch.
What do you think?

Agree - that makes sense.
Can the fixes tag be updated when pulled into the tree with:
Fixes: 199d983bc015 ("xsk: Fix crash on double free in buffer pool")

On the other hand, this was a fix for 2b43470add8c ("xsk: Introduce
AF_XDP buffer allocation API"), the original tag you have in your
patch. What should the Fixes tag point to in this case? Need some
advice please.

If I need to submit a v2 with the change please let me know.

Thanks,
Ciara

quoted

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

quoted

Fixes: 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API")

Signed-off-by: Ciara Loftus <redacted>
---
 net/xdp/xsk_buff_pool.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index bc4ad48ea4f0..fd39bb660ebc 100644
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c

@@ -83,6 +83,7 @@ struct xsk_buff_pool

*xp_create_and_assign_umem(struct xdp_sock *xs,

quoted

                xskb = &pool->heads[i];
                xskb->pool = pool;
                xskb->xdp.frame_sz = umem->chunk_size - umem->headroom;
+               INIT_LIST_HEAD(&xskb->free_list_node);
                if (pool->unaligned)
                        pool->free_heads[i] = xskb;
                else
--
2.17.1