linux-kernel - Re: [PATCH v2] staging: tidspbridge: protect dmm

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Date:	Wed, 29 Dec 2010 11:42:20 +0200
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	Felipe Contreras <felipe.contreras@...ia.com>,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	greg@...ah.com, omar.ramirez@...com, fernando.lugo@...com,
	nm@...com, ameya.palande@...ia.com, h-kanigeri2@...com
Subject: Re: [PATCH v2] staging: tidspbridge: protect dmm_map properly

On Tue, Dec 28, 2010 at 4:48 PM, Ohad Ben-Cohen <ohad@...ery.com> wrote:
> On Tue, Dec 28, 2010 at 2:12 PM, Felipe Contreras
> <felipe.contreras@...il.com> wrote:
>> On Tue, Dec 28, 2010 at 12:56 PM, Ohad Ben-Cohen <ohad@...ery.com> wrote:
>>> I still don't know how exactly you triggered the bug: is gst-dsp
>>> multithreaded ? and one of its threads invoked proc_un_map() while
>>> another thread called proc_begin_dma() ?
>>
>> I haven't investigated why that happens
>
> Btw, I still think you should look into this.
>
> The kernel panic will be solved, but you may still have a race there
> that can lead to data corruption: if proc_un_map will be fast enough,
> it will acquire the proc_lock mutex before proc_begin_dma(), and then
> you will miss a cache operation.

Aquiring the lock is the first thing done; if proc_un_map() aquires
the lock first, it's because it was run first, and thus a problem for
user-space. If user-space wants the cache operation, it must run
proc_begin_dma() first, there's nothing kernel-space can do to fix
that.

-- 
Felipe Contreras
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