netdev - Re: DM9000 issue with mem resource management

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Message-ID: <20080605174030.GM11277@trinity.fluff.org>
Date:	Thu, 5 Jun 2008 18:40:30 +0100
From:	Ben Dooks <ben-linux@...ff.org>
To:	Laurent Pinchart <laurentp@...-semaphore.com>
Cc:	netdev@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>
Subject: Re: DM9000 issue with mem resource management

On Thu, Jun 05, 2008 at 05:42:58PM +0200, Laurent Pinchart wrote:
> Hi everybody,
> 
> I ran into a resource-related bug in the DM9000 driver.
> 
> When the platform device has only 2 resources, dm9000_probe() doesn't set 
> db->irq_res, which results in a segfault when the pointer gets dereferenced 
> in dm9000_open().
> 
> I tried to fix the issue, and found out that the resource management code is 
> quite broken.

Personally, I'm thinking about just removing the case for 2, and making it
three resources only. The following in-kernel machines use the following
resources:

arch/arm/mach-at91/board-sam9261ek.c			3
arch/arm/mach-pxa/cm-x270.c				3
arch/arm/mach-pxa/em-x270.c				3
arch/arm/mach-pxa/trizeps4.c				3
arch/arm/mach-pxa/colibri.c				3
arch/arm/mach-s3c2410/mach-bast.c			3
arch/arm/mach-s3c2410/mach-vr1000.c			3
arch/blackfin/mach-bf527/boards/ezkit.c			2
arch/blackfin/mach-bf533/boards/H8606.c			2
arch/blackfin/mach-bf533/boards/ip0x.c			3
arch/blackfin/mach-bf537/boards/generic_board.c		2
arch/blackfin/mach-bf537/boards/stamp.c			2

As you can see, the #3 outweigh the #2. Unless anyone else objects, I
will add a patch to reduce this to the case where the driver expects
3 resources, and ask the users of #2 to submit changes for their
bots.
 
> If I understand things correctly, specifying 3 resources makes the DM9000 
> driver ioremap() the memory, while specifying 2 resources implies that the 
> platform code already ioremap()ed the memory. Is that right ?
> 
> If so, why does dm9000_probe() call request_mem_region() on ioremap()ed 
> memory ?

Hmm, dunno. I really have no idea why this happened. I don't think this
was my fault!
 
> Wouldn't it also be simpler to use release_mem_region() in 
> dm9000_release_board() instead of release_resource() + kfree() ?

If you already have the resource, this is a reasonably simple way of
ensuring you're disposing of the right resource.
 
> I'd be grateful if someone could confirm my assumptions. I'll then submit a 
> patch to fix those issues.

My recommendation is that we remove the 2 case completely, so I'd not bother
trying to fix this.

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.

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