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

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Message-id: <4F2F94D1.1080308@renesas.com>
Date:	Mon, 06 Feb 2012 17:52:33 +0900
From:	"Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	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 Guennadi-san,

2012/02/04 0:43, 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.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@....de>
> ---
> 
> 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.

Thank you for the patch and comments.
I also tested this patch using the g_mass_storage and g_ether.
About your points, I think so, too.
So, I will write such a code.

Best regards,
Yoshihiro Shimoda
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