[PATCH net-next 1/2] net: fix call location in kfree_skb_list_reason

Jesper Dangaard Brouer
2023-01-05T15:43:45Z

The SKB drop reason uses __builtin_return_address(0) to give the call
"location" to trace_kfree_skb() tracepoint skb:kfree_skb.

To keep this stable for compilers kfree_skb_reason() is annotated with
__fix_address (noinline __noclone) as fixed in commit c205cc7534a9
("net: skb: prevent the split of kfree_skb_reason() by gcc").

The function kfree_skb_list_reason() invoke kfree_skb_reason(), which
cause the __builtin_return_address(0) "location" to report the
unexpected address of kfree_skb_list_reason.

Example output from 'perf script':
kpktgend_0 1337 [000] 81.002597: skb:kfree_skb: skbaddr=0xffff888144824700 protocol=2048 location=kfree_skb_list_reason+0x1e reason: QDISC_DROP

Patch creates an __always_inline __kfree_skb_reason() helper call that
is called from both kfree_skb_list() and kfree_skb_list_reason().
Suggestions for solutions that shares code better are welcome.

As preparation for next patch move __kfree_skb() invocation out of
this helper function.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
net/core/skbuff.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4a0eb5593275..007a5fbe284b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -932,6 +932,21 @@ void __kfree_skb(struct sk_buff *skb)
}
EXPORT_SYMBOL(__kfree_skb);

+static __always_inline
+bool __kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
+{
+ if (unlikely(!skb_unref(skb)))
+ return false;
+
+ DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
+
+ if (reason == SKB_CONSUMED)
+ trace_consume_skb(skb);
+ else
+ trace_kfree_skb(skb, __builtin_return_address(0), reason);
+ return true;
+}
+
/**
* kfree_skb_reason - free an sk_buff with special reason
* @skb: buffer to free
@@ -944,26 +959,19 @@ EXPORT_SYMBOL(__kfree_skb);
void __fix_address
kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
{
- if (unlikely(!skb_unref(skb)))
- return;
-
- DEBUG_NET_WARN_ON_ONCE(reason <= 0 || reason >= SKB_DROP_REASON_MAX);
-
- if (reason == SKB_CONSUMED)
- trace_consume_skb(skb);
- else
- trace_kfree_skb(skb, __builtin_return_address(0), reason);
- __kfree_skb(skb);
+ if (__kfree_skb_reason(skb, reason))
+ __kfree_skb(skb);
}
EXPORT_SYMBOL(kfree_skb_reason);

-void kfree_skb_list_reason(struct sk_buff *segs,
- enum skb_drop_reason reason)
+void __fix_address
+kfree_skb_list_reason(struct sk_buff *segs, enum skb_drop_reason reason)
{
while (segs) {
struct sk_buff *next = segs->next;

- kfree_skb_reason(segs, reason);
+ if (__kfree_skb_reason(segs, reason))
+ __kfree_skb(segs);
segs = next;
}
}