Re: [PATCH 00/11] DMA sync errors

Jarek Poplawski
2010-01-21T12:44:28Z

On Wed, Jan 20, 2010 at 04:34:10PM -0800, Stephen Hemminger wrote:
> On Wed, 20 Jan 2010 16:18:05 -0800 (PST)
> David Miller <davem@davemloft.net> wrote:
>
> > From: Stephen Hemminger <shemminger@vyatta.com>
> > Date: Wed, 20 Jan 2010 15:28:32 -0800
> >
> > > This should fix the dma-debug API code (and documentation), to
> > > avoid false positives when sync is done on a partial map.
> > >
> > > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> > ...
> > > --- a/lib/dma-debug.c 2010-01-20 15:22:55.919519883 -0800
> > > +++ b/lib/dma-debug.c 2010-01-20 15:26:31.648895638 -0800
> > > @@ -285,11 +285,9 @@ static struct dma_debug_entry *hash_buck
> > > }
> > >
> > > /*
> > > - * If we have multiple matches but no perfect-fit, just return
> > > - * NULL.
> > > + * If we have multiple matches but no perfect-fit
> > > + * return best value and let caller deal with it.
> > > */
> > > - ret = (matches == 1) ? ret : NULL;
> > > -
> > > return ret;
> > > }
> > >
> >
> > I think you have to enforce a perfect-fit match for the
> > non-SYNC cases.
> >
> > check_sync() can pass in 'true' for a new bool argument "partial_ok"
> > added to hash_bucket_find() whereas check_unmap() can pass 'false'.
> >
> > get_nr_mapped_entries() should pass 'false' as well.
>
> check_unmap has checks for different size, different type,
> call_ents, direction etc.
>
> The code for get_nr_mapped_entries() is the only question;
> it is used by unmap_sg() and probably needs perfect match only.
>

Hmm... After looking at it more, mainly dma_sync_single_range()
implementations, I didn't find any reasons for these comments in
DMA-API.txt, but even if I missed something, this patch definitely
shows these lib/dma-debug warnings are buggy if they depend on the
number of mapped entries (while otherwise ref->size < entry->size
isn't reported). Btw, it seems code should try to return minimum
entry->size for such a check.

Thanks Stephen, now I feel 99.9% safe ;-)

Sorry for mistrust, David!
Jarek P.