From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 12 May 2025 09:27:22 +0000 (+0200)
Subject: net: page_pool: Don't recycle into cache on PREEMPT_RT
X-Git-Tag: v6.16-rc1~132^2~101^2~14
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=32471b2f481dea8624f27669d36ffd131d24b732;p=thirdparty%2Fkernel%2Flinux.git

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 <hawk@kernel.org>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-2-bigeasy@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 2b76848659418..974f3eef2efaf 100644
--- a/net/core/page_pool.c
+++ b/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;