netdev - [PATCH net-next 01/18] net: page_pool: Don't recycle into cache on PREEMPT

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Message-ID: <20250309144653.825351-2-bigeasy@linutronix.de>
Date: Sun,  9 Mar 2025 15:46:36 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: [PATCH net-next 01/18] 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@...nel.org>
Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/core/page_pool.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index f5e908c9e7ad8..1d669d4382729 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -800,6 +800,10 @@ 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;
 
-- 
2.47.2