4.9-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
After working on IP defragmentation lately, I found that some large packets defeat CHECKSUM_COMPLETE optimization because of NIC adding zero paddings on the last (small) fragment.
While removing the padding with pskb_trim_rcsum(), we set skb->ip_summed to CHECKSUM_NONE, forcing a full csum validation, even if all prior fragments had CHECKSUM_COMPLETE set.
We can instead compute the checksum of the part we are trimming, usually smaller than the part we keep.
Signed-off-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net (cherry picked from commit 88078d98d1bb085d72af8437707279e203524fa5) Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/skbuff.h | 5 ++--- net/core/skbuff.c | 14 ++++++++++++++ 2 files changed, 16 insertions(+), 3 deletions(-)
--- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2954,6 +2954,7 @@ static inline unsigned char *skb_push_rc return skb->data; }
+int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len); /** * pskb_trim_rcsum - trim received skb and update checksum * @skb: buffer to trim @@ -2967,9 +2968,7 @@ static inline int pskb_trim_rcsum(struct { if (likely(len >= skb->len)) return 0; - if (skb->ip_summed == CHECKSUM_COMPLETE) - skb->ip_summed = CHECKSUM_NONE; - return __pskb_trim(skb, len); + return pskb_trim_rcsum_slow(skb, len); }
static inline int __skb_trim_rcsum(struct sk_buff *skb, unsigned int len) --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1578,6 +1578,20 @@ done: } EXPORT_SYMBOL(___pskb_trim);
+/* Note : use pskb_trim_rcsum() instead of calling this directly + */ +int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len) +{ + if (skb->ip_summed == CHECKSUM_COMPLETE) { + int delta = skb->len - len; + + skb->csum = csum_sub(skb->csum, + skb_checksum(skb, len, delta, 0)); + } + return __pskb_trim(skb, len); +} +EXPORT_SYMBOL(pskb_trim_rcsum_slow); + /** * __pskb_pull_tail - advance tail of skb header * @skb: buffer to reallocate