linux-kernel - Re: [PATCH 03/16] dma-debug: add hash functions for dma_debug

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Message-Id: <20090114093918.e7b0ae46.akpm@linux-foundation.org>
Date:	Wed, 14 Jan 2009 09:39:18 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Joerg Roedel <joerg.roedel@....com>, linux-kernel@...r.kernel.org,
	mingo@...hat.com, dwmw2@...radead.org,
	fujita.tomonori@....ntt.co.jp, netdev@...r.kernel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 03/16] dma-debug: add hash functions for
 dma_debug_entries

On Wed, 14 Jan 2009 12:43:47 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Fri, 9 Jan 2009 17:19:17 +0100 Joerg Roedel <joerg.roedel@....com> wrote:
> > 
> > > +struct hash_bucket {
> > > +	struct list_head list;
> > > +	spinlock_t lock;
> > > +} ____cacheline_aligned;
> > 
> > __cacheline_aligned_in_smp.
> > 
> > This all looks like an exotically large amount of code for a debug 
> > thingy?
> 
> this code checks the DMA usage of ~1 million lines of kernel code - all 
> the DMA using drivers. I think Joerg's feature is hugely relevant as DMA 
> scribbles are one of the hardest to debug kernel bugs: they can end up in 
> permanent data corruption or other hard to find bugs. In fact i think his 
> patchset is rather simple and even having 10 times as much debug code 
> would pay for its existence in the long run.
> 

Have we previously found bugs by other means which this facility would
have detected?  I don't recall any...

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