[PATCH net-next 0/2] net: Prepare skb extensions for reuse across scrubs

Following Florian's suggestion from the discussion in [1].

The skb extension allocator retains the extension's offset after the
extension is deleted. This, in theory, allows skb_ext_add() to reuse the
existing storage instead of appending another copy when an extension is
added again.  However, it also means that we can't rely on the offset as an
indicator that the extension is present.

Make the extension cleanup safe, even when the offset is already allocated
and set, by making the individual extension put helpers idempotent, so that
they can be called multiple times.

This is preparatory work to support skb extension chunk area reuse after
skb scrubbing, which would be needed to persist BPF metadata skb extension
across scrubs [2].

[1] https://lore.kernel.org/all/ao9UV9S7rUkyQ8jv@strlen.de/ (local)
[2] https://lore.kernel.org/all/64365932-c765-472e-bf6c-b07c9ee25eaf@kernel.org/ (local)

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
Jakub Sitnicki (2):
      net: Make skb_ext_put_sp() idempotent
      net: Make skb_ext_put_mctp() idempotent

 net/core/skbuff.c | 30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)