Re: [PATCH net 1/3] igc: pad preemptible packets before reserving TX timestamps

[Eric Dumazet]

Le lun. 26 oct. 2026 à 10:16, Paul Moses <p@xxxxxxx> a écrit :
>
> Preemptible queues require software padding so hardware includes the
> padding bytes in the mCRC. Padding currently runs after TX timestamp
> reservation takes an extra skb reference. If padding needs to expand
> the skb, pskb_expand_head() rejects the shared skb.
>
> Commit c7d8bc3dd511 ("net: skbuff: don't BUG() on bad arguments to
> pskb_expand_head()") replaced the BUG_ON() with -EINVAL, exposing the
> padding error path. skb_padto() drops one reference on failure, and
> out_drop drops another. This can free the skb while the pending TX
> timestamp still holds its pointer.
>
> Move padding before TX timestamp reservation and use __skb_put_padto()
> with free_on_error set to false so out_drop handles the skb release.
> Preserve the VLAN flags in first->tx_flags when adding timestamp flags.
>
> Fixes: 17643482e9ff ("igc: add preemptible queue support in taprio")
> Signed-off-by: Paul Moses <p@xxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>