net: page_pool: Don't recycle into cache on PREEMPT_RT

With preemptible softirq and no per-CPU locking in local_bh_disable() on
PREEMPT_RT the consumer can be preempted while a skb is returned.

Avoid the race by disabling the recycle into the cache on PREEMPT_RT.

Cc: Jesper Dangaard Brouer <[email protected]>
Cc: Ilias Apalodimas <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: Sebastian Andrzej Siewior

net/core/page_pool.c

@@ -839,6 +839,10 @@ static bool page_pool_napi_local(const struct page_pool *pool)
 	const struct napi_struct *napi;
 	u32 cpuid;
 
+	/* On PREEMPT_RT the softirq can be preempted by the consumer */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		return false;
+
 	if (unlikely(!in_softirq()))
 		return false;