Re: [RFC] net: esp: fix bad handling of pages from page_pool

[Mina Almasry]

On Wed, Mar 6, 2024 at 8:09 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Wed, 6 Mar 2024 16:00:46 +0000 Dragos Tatulea wrote:
> > > Hm, that's a judgment call.
> > > Part of me wants to put it next to napi_frag_unref(), since we
> > > basically need to factor out the insides of this function.
> > > When you post the patch the page pool crowd will give us
> > > their opinions.
> >
> > Why not have napi_pp_put_page simply return false if CONFIG_PAGE_POOL is not
> > set?
>
> Without LTO it may still be a function call.
> Plus, subjectively, I think that it's a bit too much logic to encode in
> the caller (you must also check skb->pp_recycle, AFAIU)
> Maybe we should make skb_pp_recycle() take struct page and move it to
> skbuff.h ? Rename it to skb_page_unref() ?
>

Does the caller need to check skb->pp_recycle? pp_recycle seems like a
redundant bit. We can tell whether the page is pp by checking
is_pp_page(page). the pages in the frag must be pp pages when
skb->pp_recycle is set and must be non pp pages when the
skb->pp_recycle is not set, so it all seems redundant to me.

My fix would be something like:

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d577e0bee18d..cc737b7b9860 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3507,17 +3507,25 @@ int skb_cow_data_for_xdp(struct page_pool
*pool, struct sk_buff **pskb,
 bool napi_pp_put_page(struct page *page, bool napi_safe);

 static inline void
-napi_frag_unref(skb_frag_t *frag, bool recycle, bool napi_safe)
+napi_page_unref(struct page *page, bool napi_safe)
 {
-       struct page *page = skb_frag_page(frag);
-
 #ifdef CONFIG_PAGE_POOL
-       if (recycle && napi_pp_put_page(page, napi_safe))
+       if (napi_pp_put_page(page, napi_safe))
                return;
 #endif
        put_page(page);
 }

+static inline void
+napi_frag_unref(skb_frag_t *frag, bool recycle, bool napi_safe)
+{
+       struct page *page = skb_frag_page(frag);
+
+       DEBUG_NET_WARN_ON(recycle != is_pp_page(page));
+
+       napi_page_unref(page);
+}
+

And then use napi_page_unref() in the callers to handle page pool &
non-page pool gracefully without leaking page pool internals to the
callers.

> > Regarding stable would I need to send a separate fix that does the raw pp page
> > check without the API?
>
> You can put them in one patch, I reckon.



--
Thanks,
Mina