Re: Generic DMA - BUG_ON

From: Michal Simek
Date: Wed Jan 20 2010 - 06:20:11 EST

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
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 Simek, Ing. (M.Eng)
w: p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux -
Microblaze U-BOOT custodian
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