netdev - [PATCH net-next 2/4] net: dev: Remove get_cpu() in netif_rx

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Date:   Wed,  2 Feb 2022 13:28:46 +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 2/4] net: dev: Remove get_cpu() in netif_rx_internal().

The get_cpu() usage was added in commit
    b0e28f1effd1d ("net: netif_rx() must disable preemption")

because ip_dev_loopback_xmit() invoked netif_rx() with enabled preemtion
causing a warning in smp_processor_id(). The function netif_rx() should
only be invoked from an interrupt context which implies disabled
preemption. The commit
   e30b38c298b55 ("ip: Fix ip_dev_loopback_xmit()")

was addressing this and replaced netif_rx() with in netif_rx_ni() in
ip_dev_loopback_xmit().

Based on the discussion on the list, the former patch (b0e28f1effd1d)
should not have been applied only the latter (e30b38c298b55).

Remove get_cpu() since the function is supossed to be invoked from
context with stable per-CPU pointers (either by disabling preemption or
software interrupts).

Link: https://lkml.kernel.org/r/20100415.013347.98375530.davem@davemloft.net
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/core/dev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 325b70074f4ae..0d13340ed4054 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4810,8 +4810,7 @@ static int netif_rx_internal(struct sk_buff *skb)
 	{
 		unsigned int qtail;

-		ret = enqueue_to_backlog(skb, get_cpu(), &qtail);
-		put_cpu();
+		ret = enqueue_to_backlog(skb, smp_processor_id(), &qtail);
 	}
 	return ret;
 }
-- 
2.34.1