On Thu, Nov 26, 2020 at 3:19 AM Marco Elver [off-list ref] wrote:

On Wed, 25 Nov 2020 at 21:43, Jakub Kicinski [off-list ref] wrote:

quoted

On Wed, 25 Nov 2020 18:34:36 +0100 Marco Elver wrote:

quoted

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ffe3dcc0ebea..070b1077d976 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -233,6 +233,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
      skb->end = skb->tail + size;
      skb->mac_header = (typeof(skb->mac_header))~0U;
      skb->transport_header = (typeof(skb->transport_header))~0U;
+     skb_set_kcov_handle(skb, kcov_common_handle());

      /* make sure we initialize shinfo sequentially */
      shinfo = skb_shinfo(skb);

@@ -249,9 +250,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,

              fclones->skb2.fclone = SKB_FCLONE_CLONE;
      }
-
-     skb_set_kcov_handle(skb, kcov_common_handle());

Why the move?

v2 of the original series had it above. I frankly don't mind.

1. Group it with the other fields above?

2. Leave it at the end here?

quoted

quoted

 out:
      return skb;
 nodata:

@@ -285,8 +283,6 @@ static struct sk_buff *__build_skb_around(struct sk_buff *skb,
      memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
      atomic_set(&shinfo->dataref, 1);

-     skb_set_kcov_handle(skb, kcov_common_handle());
-
      return skb;
 }

And why are we dropping this?

It wasn't here originally.

quoted

If this was omitted in earlier versions it's just a independent bug,
I don't think build_skb() will call __alloc_skb(), so we need a to
set the handle here.

Correct, that was an original omission.

Will send v2.

Does it make more sense to revert the patch that added the extensions
and the follow-on fixes and add a separate new patch instead?

If adding a new field to the skb, even if only in debug builds,
please check with pahole how it affects struct layout if you
haven't yet.

The skb_extensions idea was mine. Apologies for steering
this into an apparently unsuccessful direction. Adding new fields
to skb is very rare because possibly problematic wrt allocation.