linux-kernel - Re: [PATCH/RFC] usb: fix renesas_usbhs to not schedule in atomic context

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Date:	Sun, 5 Feb 2012 16:54:00 +0200
From:	Felipe Balbi <balbi@...com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	"Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>,
	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Vinod Koul <vinod.koul@...el.com>,
	Magnus Damm <magnus.damm@...il.com>, linux-mmc@...r.kernel.org,
	alsa-devel@...a-project.org, linux-serial@...r.kernel.org,
	Paul Mundt <lethal@...ux-sh.org>, linux-usb@...r.kernel.org
Subject: Re: [PATCH/RFC] usb: fix renesas_usbhs to not schedule in atomic
 context

Hi,

On Fri, Feb 03, 2012 at 04:43:20PM +0100, Guennadi Liakhovetski wrote:
> The current renesas_usbhs driver triggers
> 
> BUG: scheduling while atomic: ksoftirqd/0/3/0x00000102
> 
> with enabled CONFIG_DEBUG_ATOMIC_SLEEP, by submitting DMA transfers from 
> an atomic (tasklet) context, which is not supported by the shdma dmaengine 
> driver. Fix it by switching to a work. Also simplify some list 
> manipulations.

you are doing much more than what you say. Also, instead of using a
workqueue, have you considered using threaded_irqs ?

(I didn't go over the driver again to see if it makes sense to use
threaded_irqs in this case, but doesn't hurt asking)

> Shimoda-san, this is the problem, that you were observing. However, it 
> exists with the present version of shdma just as well as with the new one 
> - on top of the simple DMA library. I marked it an RFC because (1) I only 
> lightly tested it with the gadget device on mackerel with the mass storage 
> gadget, and (2) I am somewhat concerned about races. Currently the work 
> function runs with no locking and there are no usual cancel_work_sync() 
> points in the patch. However, it has also been like this before with the 
> tasklet implementation, which is not much better, and it looks like there 
> are no asynchronous operations on the same packets like timeouts. Only 
> asynchronous events, that I can think about are things like unloading the 
> driver or unplugging the cable, but these have been there before too. It 
> would become worse on SMP, I think. Comments welcome.
> 
> diff --git a/drivers/usb/renesas_usbhs/fifo.c b/drivers/usb/renesas_usbhs/fifo.c
> index 72339bd..4d739ec 100644
> --- a/drivers/usb/renesas_usbhs/fifo.c
> +++ b/drivers/usb/renesas_usbhs/fifo.c
> @@ -75,8 +75,7 @@ void usbhs_pkt_push(struct usbhs_pipe *pipe, struct usbhs_pkt *pkt,
>  		pipe->handler = &usbhsf_null_handler;
>  	}
>  
> -	list_del_init(&pkt->node);
> -	list_add_tail(&pkt->node, &pipe->list);
> +	list_move_tail(&pkt->node, &pipe->list);
>  
>  	/*
>  	 * each pkt must hold own handler.
> @@ -106,7 +105,7 @@ static struct usbhs_pkt *__usbhsf_pkt_get(struct usbhs_pipe *pipe)
>  	if (list_empty(&pipe->list))
>  		return NULL;
>  
> -	return list_entry(pipe->list.next, struct usbhs_pkt, node);
> +	return list_first_entry(&pipe->list, struct usbhs_pkt, node);

these two hunks are not part of $SUBJECT

-- 
balbi

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