linux-kernel - Re: [PATCH 0/6] get rid of on-stack dma buffers

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Date:	Tue, 22 Mar 2011 15:27:30 +0100
From:	Florian Mickler <florian@...kler.org>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	Andy Walls <awalls@...metrocast.net>,
	"mchehab@...radead.org" <mchehab@...radead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"js@...uxtv.org" <js@...uxtv.org>,
	"tskd2@...oo.co.jp" <tskd2@...oo.co.jp>,
	"liplianin@...by" <liplianin@...by>,
	"g.marco@...enet.de" <g.marco@...enet.de>,
	"aet@...terburn.org" <aet@...terburn.org>,
	"pb@...uxtv.org" <pb@...uxtv.org>,
	"mkrufky@...uxtv.org" <mkrufky@...uxtv.org>,
	"nick@...k-andrew.net" <nick@...k-andrew.net>,
	"max@...eto.com" <max@...eto.com>,
	"janne-dvb@...nau.be" <janne-dvb@...nau.be>,
	Oliver Neukum <oliver@...kum.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [PATCH 0/6] get rid of on-stack dma buffers

2011/3/22 Roedel, Joerg <Joerg.Roedel@....com>:
> On Mon, Mar 21, 2011 at 05:03:15PM -0400, Florian Mickler wrote:
>> I guess (not verified), that the dma api takes sufficient precautions
>> to abort the dma transfer if a timeout happens.  So freeing _should_
>> not be an issue. (At least, I would expect big fat warnings everywhere
>> if that were the case)
>
> Freeing is very well an issue. All you can expect from the DMA-API is to
> give you a valid DMA handle for your device. But it can not prevent that
> a device uses this handle after you returned it. You need to make sure
> yourself that any pending DMA is canceled before calling kfree().

sorry, I meant usb_control_msg above when I said 'dma api'... as that
is the function these
drivers use to do the dma.

Regards,
Flo
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