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

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Message-ID: <AANLkTi=s03AA5wJaUzp7KkQDBcBVceSn4QvwH8CyRRyO@mail.gmail.com>
Date:	Wed, 29 Dec 2010 11:46:25 +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 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.

>
>> If that user thread will crash, drv_remove_all_resources() will clean
>> up all map_obj's.
>
> Not if a proc_*_dma() is still running.

It will be called after it will return, and its thread will exit (or crash).
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