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

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Message-ID: <AANLkTik1T_CktRwQz0JjTAY0s1hOOage=veOo1-Cb3Pn@mail.gmail.com>
Date:	Wed, 29 Dec 2010 12:06:24 +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 Wed, Dec 29, 2010 at 11:46 AM, Ohad Ben-Cohen <ohad@...ery.com> wrote:
> On Wed, Dec 29, 2010 at 11:39 AM, Felipe Contreras
> <felipe.contreras@...il.com> wrote:
>> On Tue, Dec 28, 2010 at 2:37 PM, Ohad Ben-Cohen <ohad@...ery.com> wrote:
>>> On Tue, Dec 28, 2010 at 2:24 PM, Felipe Contreras
>>> <felipe.contreras@...il.com> wrote:
>>>> user-space crashed, not kernel-space; the code would continue to run
>>>> and eventually release the lock.
>>>
>>> So you'll have to be more specific about the scenario you are describing.
>>>
>>> If there's a user thread that is still running the proc_*_dma()
>>> function, and we agree that this thread keeps running until completion
>>> and then returns to user space, what's the problem ?
>>
>> The problem is if the user-space process crashes exactly in the middle
>> of it, *before* completing. With locks there's no problem, as
>> proc_un_map() would wait for the lock in my patch. In your patch it
>> would not wait, just return -EBUSY.
>
> We have two threads.
>
> One called proc_un_map(), and one called proc_begin_dma().
>
> The first crashed, but the second didn't. it still holds the bridge
> device open. When it will exit, and release the device, then
> drv_remove_all_resources() will be called, and all the map_obj's will
> be cleaned.

I'm not familiar how crashes are handled; if you say as long as one
task is still running the device release is not called, then I guess
there's no issue.

-- 
Felipe Contreras
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