net: mirror skb frag ref/unref helpers

Refactor some of the skb frag ref/unref helpers for improved clarity.

Implement napi_pp_get_page() to be the mirror counterpart of
napi_pp_put_page().

Implement skb_page_ref() to be the mirror of skb_page_unref().

Improve __skb_frag_ref() to become a mirror counterpart of
__skb_frag_unref(). Previously unref could handle pp & non-pp pages,
while the ref could only handle non-pp pages. Now both the ref & unref
helpers can correctly handle both pp & non-pp pages.

Now that __skb_frag_ref() can handle both pp & non-pp pages, remove
skb_pp_frag_ref(), and use __skb_frag_ref() instead.  This lets us
remove pp specific handling from skb_try_coalesce.

Additionally, since __skb_frag_ref() can now handle both pp & non-pp
pages, a latent issue in skb_shift() should now be fixed. Previously
this function would do a non-pp ref & pp unref on potential pp frags
(fragfrom). After this patch, skb_shift() should correctly do a pp
ref/unref on pp frags.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240410190505.1225848-3-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 35 insertions, 4 deletions

diff --git a/include/linux/skbuff_ref.h b/include/linux/skbuff_ref.h
index 11f0a4063403..4dcdbe9fbc5f 100644
--- a/include/linux/skbuff_ref.h
+++ b/include/linux/skbuff_ref.h
@@ -8,16 +8,47 @@
 #define _LINUX_SKBUFF_REF_H
 
 #include <linux/skbuff.h>
+#include <net/page_pool/helpers.h>
+
+#ifdef CONFIG_PAGE_POOL
+static inline bool is_pp_page(struct page *page)
+{
+	return (page->pp_magic & ~0x3UL) == PP_SIGNATURE;
+}
+
+static inline bool napi_pp_get_page(struct page *page)
+{
+	page = compound_head(page);
+
+	if (!is_pp_page(page))
+		return false;
+
+	page_pool_ref_page(page);
+	return true;
+}
+#endif
+
+static inline void skb_page_ref(struct page *page, bool recycle)
+{
+#ifdef CONFIG_PAGE_POOL
+	if (recycle && napi_pp_get_page(page))
+		return;
+#endif
+	get_page(page);
+}
 
 /**
  * __skb_frag_ref - take an addition reference on a paged fragment.
  * @frag: the paged fragment
+ * @recycle: skb->pp_recycle param of the parent skb. False if no parent skb.
  *
- * Takes an additional reference on the paged fragment @frag.
+ * Takes an additional reference on the paged fragment @frag. Obtains the
+ * correct reference count depending on whether skb->pp_recycle is set and
+ * whether the frag is a page pool frag.
  */
-static inline void __skb_frag_ref(skb_frag_t *frag)
+static inline void __skb_frag_ref(skb_frag_t *frag, bool recycle)
 {
-	get_page(skb_frag_page(frag));
+	skb_page_ref(skb_frag_page(frag), recycle);
 }
 
 /**
@@ -29,7 +60,7 @@ static inline void __skb_frag_ref(skb_frag_t *frag)
  */
 static inline void skb_frag_ref(struct sk_buff *skb, int f)
 {
-	__skb_frag_ref(&skb_shinfo(skb)->frags[f]);
+	__skb_frag_ref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
 }
 
 bool napi_pp_put_page(struct page *page);