From: Michal Simek <monstr@monstr.eu>
To: Joerg Roedel <joerg.roedel@amd.com>
Cc: linux-kernel@vger.kernel.org, michal.simek@petalogix.com,
arnd@arndb.de, linux-arch@vger.kernel.org,
fujita.tomonori@lab.ntt.co.jp, akpm@linux-foundation.org,
mingo@elte.hu
Subject: Re: Generic DMA - BUG_ON
Date: Wed, 20 Jan 2010 12:18:04 +0100 [thread overview]
Message-ID: <4B56E66C.50004@monstr.eu> (raw)
In-Reply-To: <20100120110031.GD8665@amd.com>
Joerg Roedel wrote:
> On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote:
>> and ops is NULL, then this code will oops; you will get a full register
>> dump and backtrace. You can use this information along with markup_oops.pl
>> to find out where the problem is.
>
> You can't rely on the oops if the code runs in process context. The
> process may have address 0 mapped which would result in a security hole.
> We had two of these bugs last year.
That's the same problem which I had some days ago and Microblaze misses
valuable backtrace (because we don't have FP or constant frame size).
>
> But I don't see any point in checking for dma_ops != NULL too. Any
> developer would mention such a bug long before init is started.
I agree that checking adds extra cycles to every dma-api call.
I like as wrote Russel to check if ops exists or not.
Let's look at code which is there.
dma_map_single_attrs - calls ops->map_page without any checking
The same for dma_map_sg_attrs, dma_map_page
The rest of functions is ok. If any checking will be there, I don't have
any problem with it.
Michal
>
> Joerg
>
>
--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
next prev parent reply other threads:[~2010-01-20 11:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-20 10:08 Generic DMA - BUG_ON monstr
2010-01-20 10:08 ` [PATCH] asm-generic: dma: Add BUG_ON for uninitialized dma_ops monstr
2010-01-20 10:48 ` Alexey Dobriyan
2010-01-20 11:00 ` Geert Uytterhoeven
2010-01-20 10:56 ` Joerg Roedel
2010-01-22 1:11 ` FUJITA Tomonori
2010-01-20 10:53 ` Generic DMA - BUG_ON Russell King
2010-01-20 11:00 ` Joerg Roedel
2010-01-20 11:18 ` Michal Simek [this message]
2010-01-20 19:03 ` Arnd Bergmann
2010-01-21 15:51 ` Steven J. Magnani
2010-01-21 17:53 ` Russell King
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