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

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Message-ID: <AANLkTi=X=Av0SaqphXUfiXMNX_tD8OF1CWes34keZ8O1@mail.gmail.com>
Date:	Tue, 28 Dec 2010 16:48:46 +0200
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	Felipe Contreras <felipe.contreras@...il.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 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.
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