netdev - [PATCH net-next 1/4] net: dev: Remove the preempt_disable() in netif_rx

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Date:   Wed,  2 Feb 2022 13:28:45 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     bpf@...r.kernel.org, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH net-next 1/4] net: dev: Remove the preempt_disable() in netif_rx_internal().

The preempt_disable() and rcu_disable() section was introduced in commit
   bbbe211c295ff ("net: rcu lock and preempt disable missing around generic xdp")

The backtrace shows that bottom halves were disabled and so the usage of
smp_processor_id() would not trigger a warning.
The "suspicious RCU usage" warning was triggered because
rcu_dereference() was not used in rcu_read_lock() section (only
rcu_read_lock_bh()). A rcu_read_lock() is sufficient.

Remove the preempt_disable() statement which is not needed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/core/dev.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 1baab07820f65..325b70074f4ae 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4796,7 +4796,6 @@ static int netif_rx_internal(struct sk_buff *skb)
 		struct rps_dev_flow voidflow, *rflow = &voidflow;
 		int cpu;
 
-		preempt_disable();
 		rcu_read_lock();
 
 		cpu = get_rps_cpu(skb->dev, skb, &rflow);
@@ -4806,7 +4805,6 @@ static int netif_rx_internal(struct sk_buff *skb)
 		ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
 
 		rcu_read_unlock();
-		preempt_enable();
 	} else
 #endif
 	{
-- 
2.34.1