net: Kill skb_truesize_check(), it only catches false-positives.

A long time ago we had bugs, primarily in TCP, where we would modify
skb->truesize (for TSO queue collapsing) in ways which would corrupt
the socket memory accounting.

skb_truesize_check() was added in order to try and catch this error
more systematically.

However this debugging check has morphed into a Frankenstein of sorts
and these days it does nothing other than catch false-positives.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -416,15 +416,6 @@ extern void	      skb_over_panic(struct sk_buff *skb, int len,
 				     void *here);
 extern void	      skb_under_panic(struct sk_buff *skb, int len,
 				      void *here);
-extern void	      skb_truesize_bug(struct sk_buff *skb);
-
-static inline void skb_truesize_check(struct sk_buff *skb)
-{
-	int len = sizeof(struct sk_buff) + skb->len;
-
-	if (unlikely((int)skb->truesize < len))
-		skb_truesize_bug(skb);
-}
 
 extern int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
 			int getfrag(void *from, char *to, int offset,

include/net/sock.h

@@ -860,7 +860,6 @@ static inline void sk_mem_uncharge(struct sock *sk, int size)
 
 static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
 {
-	skb_truesize_check(skb);
 	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
 	sk->sk_wmem_queued -= skb->truesize;
 	sk_mem_uncharge(sk, skb->truesize);

net/core/skbuff.c

@@ -143,14 +143,6 @@ void skb_under_panic(struct sk_buff *skb, int sz, void *here)
 	BUG();
 }
 
-void skb_truesize_bug(struct sk_buff *skb)
-{
-	WARN(net_ratelimit(), KERN_ERR "SKB BUG: Invalid truesize (%u) "
-	       "len=%u, sizeof(sk_buff)=%Zd\n",
-	       skb->truesize, skb->len, sizeof(struct sk_buff));
-}
-EXPORT_SYMBOL(skb_truesize_bug);
-
 /* 	Allocate a new skbuff. We do this ourselves so we can fill in a few
  *	'private' fields and also do memory statistics to find all the
  *	[BEEP] leaks.

net/core/sock.c

@@ -1137,7 +1137,6 @@ void sock_rfree(struct sk_buff *skb)
 {
 	struct sock *sk = skb->sk;
 
-	skb_truesize_check(skb);
 	atomic_sub(skb->truesize, &sk->sk_rmem_alloc);
 	sk_mem_uncharge(skb->sk, skb->truesize);
 }