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

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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: Menglong Dong <imagedong@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Menglong Dong 2022-08-21 13:18:58 +08:00 committed by David S. Miller
parent fa2bc96259
commit c205cc7534
3 changed files with 12 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
include/linux/compiler_attributes.h
View file

@ -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 */

3
include/linux/skbuff.h
View file

@ -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

5
net/core/skbuff.c
View file

@ -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);