[PATCH v4] dma-debug: New interfaces to debug dma mapping errors
Andrew Morton
akpm at linux-foundation.org
Tue Oct 9 21:02:15 UTC 2012
On Mon, 08 Oct 2012 11:07:20 -0600
Shuah Khan <shuah.khan at 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.
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