Commit c205cc75 authored by Menglong Dong's avatar Menglong Dong Committed by David S. Miller
Browse files

net: skb: prevent the split of kfree_skb_reason() by gcc 



Sometimes, gcc will optimize the function by spliting it to two or
more functions. In this case, kfree_skb_reason() is splited to
kfree_skb_reason and kfree_skb_reason.part.0. However, the
function/tracepoint trace_kfree_skb() in it needs the return address
of kfree_skb_reason().

This split makes the call chains becomes:
  kfree_skb_reason() -> kfree_skb_reason.part.0 -> trace_kfree_skb()

which makes the return address that passed to trace_kfree_skb() be
kfree_skb().

Therefore, introduce '__fix_address', which is the combination of
'__noclone' and 'noinline', and apply it to kfree_skb_reason() to
prevent to from being splited or made inline.

(Is it better to simply apply '__noclone oninline' to kfree_skb_reason?
I'm thinking maybe other functions have the same problems)

Meanwhile, wrap 'skb_unref()' with 'unlikely()', as the compiler thinks
it is likely return true and splits kfree_skb_reason().

Signed-off-by: default avatarMenglong Dong <imagedong@tencent.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fa2bc962

include/linux/compiler_attributes.h

+7 −0
Original line number Diff line number Diff line
@@ -371,4 +371,11 @@ 
 */

#define __weak                          __attribute__((__weak__))



/*

 * Used by functions that use '__builtin_return_address'. These function

 * don't want to be splited or made inline, which can make

 * the '__builtin_return_address' get unexpected address.

 */

#define __fix_address noinline __noclone



#endif /* __LINUX_COMPILER_ATTRIBUTES_H */

include/linux/skbuff.h

+2 −1
Original line number Diff line number Diff line
@@ -1195,7 +1195,8 @@ static inline bool skb_unref(struct sk_buff *skb) 
	return true;

}



void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);

void __fix_address

kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);



/**

 *	kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason

net/core/skbuff.c

+3 −2
Original line number Diff line number Diff line
@@ -777,9 +777,10 @@ EXPORT_SYMBOL(__kfree_skb); 
 *	hit zero. Meanwhile, pass the drop reason to 'kfree_skb'

 *	tracepoint.

 */

void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)

void __fix_address

kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)

{

	if (!skb_unref(skb))

	if (unlikely(!skb_unref(skb)))

		return;



	DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);