Message-ID: <1349905825.5993.2.camel@lorien2>
Subject: Re: [PATCH v4] dma-debug: New interfaces to debug dma mapping errors
From: Shuah Khan <shuah.khan@hp.com>
Reply-To: shuah.khan@hp.com
To: Andrew Morton <akpm@linux-foundation.org>
Cc: konrad.wilk@oracle.com, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, rob@landley.net, stern@rowland.harvard.edu,
        joerg.roedel@amd.com, bhelgaas@google.com,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        devel@linuxdriverproject.org, x86@kernel.org, shuahkhan@gmail.com
Date: Wed, 10 Oct 2012 15:50:25 -0600
In-Reply-To: <20121009140215.5c0a65c9.akpm@linux-foundation.org>
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On Tue, 2012-10-09 at 14:02 -0700, Andrew Morton wrote:
> On Mon, 08 Oct 2012 11:07:20 -0600
> Shuah Khan <shuah.khan@hp.com> wrote:
> 
> > > 
> > > Still seems overly complicated to me, but whatev.
> > > 
> > > I think the way to handle this is pretty simple: set a flag in the dma
> > > entry when someone runs dma_mapping_error() and, if that flag wasn't
> > > set at unmap time, emit a loud warning.
> > > 
> > > From my reading of the code, this patch indeed does that, along with a
> > > bunch of other (unnecessary?) stuff.  But boy, the changelog conceals
> > > this information well!
> > 
> > Are you referring to the system wide error counters when you say
> > unnecessary stuff. The reason I added those was to catch errors when
> > drivers don't do unmap. Several drivers fail to do unmap. Checking flag
> > from unmap debug interfaces, doesn't cover these cases. However, I think
> > the value of system wide counters is limited in the sense that they
> > don't really identify the driver that needs fixing. In that sense it can
> > be deemed unnecessary. I dropped them in v5 patch, which I am sending
> > out.
> 
> hm.  Could we keep a counter of the number of map/unmap calls within
> the dma object and then emit a warning if that is non-zero at teardown
> time?  That should identify the offending driver.
> 

Thanks. That would work. Will take a look and see what it takes to
implement.

-- Shuah


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