netdev - Re: [PATCH 5/5] net: sh

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Date:	Fri, 16 Mar 2012 19:46:28 +0900
From:	"Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH 5/5] net: sh_eth: use NAPI

2012/03/16 18:15, David Miller wrote:
> From: "Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
> Date: Fri, 16 Mar 2012 17:46:18 +0900
> 
> sh_eth_interrupt takes mdp->lock, and:
> 
>> +static int sh_eth_poll(struct napi_struct *napi, int budget)
>> +{
>> +	struct sh_eth_private *mdp = container_of(napi, struct sh_eth_private,
>> +						  napi);
>> +	struct net_device *ndev = mdp->ndev;
>> +	struct sh_eth_cpu_data *cd = mdp->cd;
>> +	int work_done = 0, txfree_num;
>> +	u32 intr_status = sh_eth_read(ndev, EESR);
>> +
>> +	spin_lock(&mdp->lock);
> 
> sh_eth_poll() runs from software interrupt context, therefore
> this can deadlock.

Thank you for the point. I will fix it.

> Even though you turned off interrupts in sh_eth_interrupt to
> enable NAPI mode, this can still happen, interrupts can be
> stuck in the interrupt controller, another device can be on
> the same interrupt line, etc.  Therefore you must handle
> this properly.

I see. I wrote a comment below in sh_eth_interrupt, but this
is a wrong comment.

+			/* Disable all interrupts */
+			sh_eth_write(ndev, 0, EESIPR);

It only disable the interrupts of the controller's channel.
It doesn't disable other devices. So, I will fix the comment.

> I would suggest _NOT_ fixing this by taking the lock with interrupts
> disabled in sh_eth_poll(), that defeats the whole prupose of
> converting to NAPI and this would also require you to change back
> the dev_kfree_skb() to dev_kfree_skb_irq().

I understood it. I will fix it.

> Instead, do what other drivers do, make your interrupt handler run
> completely lockless and have a sophisticated quiescence sequence
> when you want to sync interrupts off and make sure no async contexts
> are still running in the interrupt handler.  See tg3.c for one
> example of this.

Thank you for your suggestion. I will see the tg3.c.

> I'm toss this entire patch series, it needs a lot more work.

I understood it. I wlll resubmit entire patch series after I fix the code.

Best regards,
Yoshihiro Shimoda
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