Re: [PATCH net-next 3/4] net: dev: Makes sure netif_rx() can be invoked in any context.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-02-03 07:25:01 [-0800], Eric Dumazet wrote:
> 
> No, the loopback device (ifconfig log) I am referring to is in
> drivers/net/loopback.c
> 
> loopback_xmit() calls netif_rx() directly, while bh are already disabled.

ah okay. Makes sense.

> Instead of adding a local_bh_disable()/local_bh_enable() in netif_rx()
> I suggested
> to rename current netif_rx() to __netif_rx() and add a wrapper, eg :

So we still end up with two interfaces. Do I move a few callers like the
one you already mentioned over to the __netif_rx() interface or will it
be the one previously mentioned for now?

Would something like 

diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h
index fc53e0ad56d90..561cbca431ca6 100644
--- a/include/linux/bottom_half.h
+++ b/include/linux/bottom_half.h
@@ -30,7 +30,12 @@ static inline void local_bh_enable_ip(unsigned long ip)
 
 static inline void local_bh_enable(void)
 {
-	__local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
+	if (unlikely(softirq_count() == SOFTIRQ_DISABLE_OFFSET)) {
+		__local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
+	} else {
+		preempt_count_sub(SOFTIRQ_DISABLE_OFFSET);
+		barrier();
+	}
 }
 
 #ifdef CONFIG_PREEMPT_RT

lower the overhead to acceptable range? (I still need to sell this to
peterz first).

Sebastian