netdev - [PATCH net-next] net: Correct wrong BH disable in hard-interrupt.

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Date:   Wed, 16 Feb 2022 18:50:46 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        "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>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH net-next] net: Correct wrong BH disable in hard-interrupt.

I missed the obvious case where netif_ix() is invoked from hard-IRQ
context.

Disabling bottom halves is only needed in process context. This ensures
that the code remains on the current CPU and that the soft-interrupts
are processed at local_bh_enable() time.
In hard- and soft-interrupt context this is already the case and the
soft-interrupts will be processed once the context is left (at irq-exit
time).

Disable bottom halves if neither hard-interrupts nor soft-interrupts are
disabled. Update the kernel-doc, mention that interrupts must be enabled
if invoked from process context.

Fixes: baebdf48c3600 ("net: dev: Makes sure netif_rx() can be invoked in any context.")
Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
Marek, does this work for you?

 net/core/dev.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 909fb38159108..87729491460fc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4860,7 +4860,9 @@ EXPORT_SYMBOL(__netif_rx);
  *	congestion control or by the protocol layers.
  *	The network buffer is passed via the backlog NAPI device. Modern NIC
  *	driver should use NAPI and GRO.
- *	This function can used from any context.
+ *	This function can used from interrupt and from process context. The
+ *	caller from process context must not disable interrupts before invoking
+ *	this function.
  *
  *	return values:
  *	NET_RX_SUCCESS	(no congestion)
@@ -4870,12 +4872,15 @@ EXPORT_SYMBOL(__netif_rx);
 int netif_rx(struct sk_buff *skb)
 {
 	int ret;
+	bool need_bh_off = !(hardirq_count() | softirq_count());
 
-	local_bh_disable();
+	if (need_bh_off)
+		local_bh_disable();
 	trace_netif_rx_entry(skb);
 	ret = netif_rx_internal(skb);
 	trace_netif_rx_exit(ret);
-	local_bh_enable();
+	if (need_bh_off)
+		local_bh_enable();
 	return ret;
 }
 EXPORT_SYMBOL(netif_rx);
-- 
2.34.1