Commit c04de0c7 authored by Eric Dumazet's avatar Eric Dumazet Committed by Paolo Abeni
Browse files

net: avoid prefetching NULL pointers 



Aditya Gupta reported PowerPC crashes bisected to the blamed commit.

Apparently some platforms do not allow prefetch() on arbitrary pointers.

  prefetch(next);
  prefetch(&next->priority); // CRASH when next == NULL

Only NULL seems to be supported, with specific handling in prefetch().

Add a conditional to avoid the two prefetches and the skb->next clearing
for the last skb in the list.

Fixes: b2e9821c ("net: prefech skb->priority in __dev_xmit_skb()")
Reported-by: default avatarAditya Gupta <adityag@linux.ibm.com>
Closes: https://lore.kernel.org/netdev/e9f4abee-b132-440f-a50e-bced0868b5a7@linux.ibm.com/T/#mddc372b64ec5a3b181acc9ee3909110c391cc18a


Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Tested-by: default avatarAditya Gupta <adityag@linux.ibm.com>
Link: https://patch.msgid.link/20251218081844.809008-1-edumazet@google.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent f79f9b7a

net/core/dev.c

+5 −3
Original line number Diff line number Diff line
@@ -4241,9 +4241,11 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, 
		int count = 0;



		llist_for_each_entry_safe(skb, next, ll_list, ll_node) {

			if (next) {

				prefetch(next);

				prefetch(&next->priority);

				skb_mark_not_on_list(skb);

			}

			rc = dev_qdisc_enqueue(skb, q, &to_free, txq);

			count++;

		}