Revert "net: mirror skb frag ref/unref helpers"

This reverts commit a580ea9.

This revert is to resolve Dragos's report of page_pool leak here:
https://lore.kernel.org/lkml/20240424165646.1625690-2-dtatulea@nvidia.com/

The reverted patch interacts very badly with commit 2cc3aeb ("skbuff:
Fix a potential race while recycling page_pool packets"). The reverted
commit hopes that the pp_recycle + is_pp_page variables do not change
between the skb_frag_ref and skb_frag_unref operation. If such a change
occurs, the skb_frag_ref/unref will not operate on the same reference type.
In the case of Dragos's report, the grabbed ref was a pp ref, but the unref
was a page ref, because the pp_recycle setting on the skb was changed.

Attempting to fix this issue on the fly is risky. Lets revert and I hope
to reland this with better understanding and testing to ensure we don't
regress some edge case while streamlining skb reffing.

Fixes: a580ea9 ("net: mirror skb frag ref/unref helpers")
Reported-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Link: https://lore.kernel.org/r/20240502175423.2456544-1-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: mina

drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c

@@ -1659,7 +1659,7 @@ static void chcr_ktls_copy_record_in_skb(struct sk_buff *nskb,
 	for (i = 0; i < record->num_frags; i++) {
 		skb_shinfo(nskb)->frags[i] = record->frags[i];
 		/* increase the frag ref count */
-		__skb_frag_ref(&skb_shinfo(nskb)->frags[i], nskb->pp_recycle);
+		__skb_frag_ref(&skb_shinfo(nskb)->frags[i]);
 	}
 
 	skb_shinfo(nskb)->nr_frags = record->num_frags;

drivers/net/ethernet/sun/cassini.c

@@ -2000,7 +2000,7 @@ static int cas_rx_process_pkt(struct cas *cp, struct cas_rx_comp *rxc,
 		skb->len      += hlen - swivel;
 
 		skb_frag_fill_page_desc(frag, page->buffer, off, hlen - swivel);
-		__skb_frag_ref(frag, skb->pp_recycle);
+		__skb_frag_ref(frag);
 
 		/* any more data? */
 		if ((words[0] & RX_COMP1_SPLIT_PKT) && ((dlen -= hlen) > 0)) {
@@ -2024,7 +2024,7 @@ static int cas_rx_process_pkt(struct cas *cp, struct cas_rx_comp *rxc,
 			frag++;
 
 			skb_frag_fill_page_desc(frag, page->buffer, 0, hlen);
-			__skb_frag_ref(frag, skb->pp_recycle);
+			__skb_frag_ref(frag);
 			RX_USED_ADD(page, hlen + cp->crc_size);
 		}
 

drivers/net/veth.c

@@ -717,7 +717,7 @@ static void veth_xdp_get(struct xdp_buff *xdp)
 		return;
 
 	for (i = 0; i < sinfo->nr_frags; i++)
-		__skb_frag_ref(&sinfo->frags[i], false);
+		__skb_frag_ref(&sinfo->frags[i]);
 }
 
 static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,

include/linux/skbuff_ref.h

@@ -8,47 +8,16 @@
 #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. Obtains the
- * correct reference count depending on whether skb->pp_recycle is set and
- * whether the frag is a page pool frag.
+ * Takes an additional reference on the paged fragment @frag.
  */
-static inline void __skb_frag_ref(skb_frag_t *frag, bool recycle)
+static inline void __skb_frag_ref(skb_frag_t *frag)
 {
-	skb_page_ref(skb_frag_page(frag), recycle);
+	get_page(skb_frag_page(frag));
 }
 
 /**
@@ -60,7 +29,7 @@ static inline void __skb_frag_ref(skb_frag_t *frag, bool recycle)
  */
 static inline void skb_frag_ref(struct sk_buff *skb, int f)
 {
-	__skb_frag_ref(&skb_shinfo(skb)->frags[f], skb->pp_recycle);
+	__skb_frag_ref(&skb_shinfo(skb)->frags[f]);
 }
 
 bool napi_pp_put_page(struct page *page);

net/core/skbuff.c

@@ -904,6 +904,11 @@ static void skb_clone_fraglist(struct sk_buff *skb)
 		skb_get(list);
 }
 
+static bool is_pp_page(struct page *page)
+{
+	return (page->pp_magic & ~0x3UL) == PP_SIGNATURE;
+}
+
 int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
 		    unsigned int headroom)
 {
@@ -1025,6 +1030,37 @@ static bool skb_pp_recycle(struct sk_buff *skb, void *data)
 	return napi_pp_put_page(virt_to_page(data));
 }
 
+/**
+ * skb_pp_frag_ref() - Increase fragment references of a page pool aware skb
+ * @skb:	page pool aware skb
+ *
+ * Increase the fragment reference count (pp_ref_count) of a skb. This is
+ * intended to gain fragment references only for page pool aware skbs,
+ * i.e. when skb->pp_recycle is true, and not for fragments in a
+ * non-pp-recycling skb. It has a fallback to increase references on normal
+ * pages, as page pool aware skbs may also have normal page fragments.
+ */
+static int skb_pp_frag_ref(struct sk_buff *skb)
+{
+	struct skb_shared_info *shinfo;
+	struct page *head_page;
+	int i;
+
+	if (!skb->pp_recycle)
+		return -EINVAL;
+
+	shinfo = skb_shinfo(skb);
+
+	for (i = 0; i < shinfo->nr_frags; i++) {
+		head_page = compound_head(skb_frag_page(&shinfo->frags[i]));
+		if (likely(is_pp_page(head_page)))
+			page_pool_ref_page(head_page);
+		else
+			page_ref_inc(head_page);
+	}
+	return 0;
+}
+
 static void skb_kfree_head(void *head, unsigned int end_offset)
 {
 	if (end_offset == SKB_SMALL_HEAD_HEADROOM)
@@ -4160,7 +4196,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
 			to++;
 
 		} else {
-			__skb_frag_ref(fragfrom, skb->pp_recycle);
+			__skb_frag_ref(fragfrom);
 			skb_frag_page_copy(fragto, fragfrom);
 			skb_frag_off_copy(fragto, fragfrom);
 			skb_frag_size_set(fragto, todo);
@@ -4810,7 +4846,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 			}
 
 			*nskb_frag = (i < 0) ? skb_head_frag_to_page_desc(frag_skb) : *frag;
-			__skb_frag_ref(nskb_frag, nskb->pp_recycle);
+			__skb_frag_ref(nskb_frag);
 			size = skb_frag_size(nskb_frag);
 
 			if (pos < offset) {
@@ -5941,8 +5977,10 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 	/* if the skb is not cloned this does nothing
 	 * since we set nr_frags to 0.
 	 */
-	for (i = 0; i < from_shinfo->nr_frags; i++)
-		__skb_frag_ref(&from_shinfo->frags[i], from->pp_recycle);
+	if (skb_pp_frag_ref(from)) {
+		for (i = 0; i < from_shinfo->nr_frags; i++)
+			__skb_frag_ref(&from_shinfo->frags[i]);
+	}
 
 	to->truesize += delta;
 	to->len += len;

net/tls/tls_device_fallback.c

@@ -278,7 +278,7 @@ static int fill_sg_in(struct scatterlist *sg_in,
 	for (i = 0; remaining > 0; i++) {
 		skb_frag_t *frag = &record->frags[i];
 
-		__skb_frag_ref(frag, false);
+		__skb_frag_ref(frag);
 		sg_set_page(sg_in + i, skb_frag_page(frag),
 			    skb_frag_size(frag), skb_frag_off(frag));