netdev - Re: [PATCH 2/2] net: ks8851: Handle softirqs at the end of IRQ thread to fix hang

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Date: Tue, 2 Apr 2024 19:38:26 +0200
From: Marek Vasut <marex@...x.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>,
 Eric Dumazet <edumazet@...gle.com>, Mark Brown <broonie@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Ronald Wahl <ronald.wahl@...itan.com>,
 Simon Horman <horms@...nel.org>
Subject: Re: [PATCH 2/2] net: ks8851: Handle softirqs at the end of IRQ thread
 to fix hang

On 4/2/24 6:06 AM, Jakub Kicinski wrote:
> On Sun, 31 Mar 2024 16:21:46 +0200 Marek Vasut wrote:
>> diff --git a/drivers/net/ethernet/micrel/ks8851_common.c b/drivers/net/ethernet/micrel/ks8851_common.c
>> index 896d43bb8883d..b6b727e651f3d 100644
>> --- a/drivers/net/ethernet/micrel/ks8851_common.c
>> +++ b/drivers/net/ethernet/micrel/ks8851_common.c
>> @@ -299,7 +299,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
>>   					ks8851_dbg_dumpkkt(ks, rxpkt);
>>   
>>   				skb->protocol = eth_type_trans(skb, ks->netdev);
>> -				netif_rx(skb);
>> +				__netif_rx(skb);
> 
> maybe return the packets from ks8851_rx_pkts()
> (you can put them on a queue / struct sk_buff_head)
> and process them once the lock is released?

I think that's what netif_rx() basically already does internally in 
netif_rx_internal():

enqueue_to_backlog(skb, smp_processor_id(), &qtail);

> Also why not NAPI?

I am not quite sure what to answer here. Are you asking me to add NAPI 
support to the driver ?

>>   				ks->netdev->stats.rx_packets++;
>>   				ks->netdev->stats.rx_bytes += rxlen;
>> @@ -325,11 +325,15 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
>>    */
>>   static irqreturn_t ks8851_irq(int irq, void *_ks)
>>   {
>> +	bool need_bh_off = !(hardirq_count() | softirq_count());
> 
> I don't think IRQ / RT developers look approvingly at uses of such
> low level macros in drivers.

I _think_ the need_bh_off will be always true as Ratheesh suggested, so 
this can be dropped. I will test that before doing a V2.