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net: avoid prefetching NULL pointers

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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: b2e9821cff ("net: prefech skb->priority in __dev_xmit_skb()")
Reported-by: Aditya Gupta <adityag@linux.ibm.com>
Closes: https://lore.kernel.org/netdev/e9f4abee-b132-440f-a50e-bced0868b5a7@linux.ibm.com/T/#mddc372b64ec5a3b181acc9ee3909110c391cc18a
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Aditya Gupta <adityag@linux.ibm.com>
Link: https://patch.msgid.link/20251218081844.809008-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2025-12-18 08:18:44 +00:00 • committed by Paolo Abeni
parent f79f9b7ace
commit c04de0c795
1 changed files with 5 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

8
net/core/dev.c
View file

@ -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) {
prefetch(next);
prefetch(&next->priority);
skb_mark_not_on_list(skb);
if (next) {
prefetch(next);
prefetch(&next->priority);
skb_mark_not_on_list(skb);
}
rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
count++;
}