On Thu, 26 Nov 2020 at 17:35, Willem de Bruijn
[off-list ref] wrote:

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

[...]

quoted

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?

That doesn't work, because then we'll end up with a build-broken
commit in between the reverts and the new version, because mac80211
uses skb_get_kcov_handle().

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.

Without KCOV:

        /* size: 224, cachelines: 4, members: 72 */
        /* sum members: 217, holes: 1, sum holes: 2 */
        /* sum bitfield members: 36 bits, bit holes: 2, sum bit holes: 4 bits */
        /* forced alignments: 2 */
        /* last cacheline: 32 bytes */

With KCOV:

        /* size: 232, cachelines: 4, members: 73 */
        /* sum members: 225, holes: 1, sum holes: 2 */
        /* sum bitfield members: 36 bits, bit holes: 2, sum bit holes: 4 bits */
        /* forced alignments: 2 */
        /* last cacheline: 40 bytes */

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.