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

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Toke Høiland-Jørgensen" <toke@toke.dk>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>
Subject: [PATCH net-next] net: Correct wrong BH disable in hard-interrupt.
Date: Wed, 16 Feb 2022 18:50:46 +0100	[thread overview]
Message-ID: <Yg05duINKBqvnxUc@linutronix.de> (raw)

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@samsung.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.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

