[PATCH 03/10] x86: add initialization code for DMA-API debugging
Joerg Roedel
joerg.roedel at amd.com
Fri Nov 21 09:10:04 PST 2008
On Fri, Nov 21, 2008 at 05:56:28PM +0100, Ingo Molnar wrote:
> > + return (entry->dev_addr >> HASH_FN_SHIFT) & HASH_FN_MASK;
> > +}
> > +
> > +static struct dma_debug_entry *dma_entry_alloc(void)
> > +{
> > + gfp_t gfp = GFP_KERNEL | __GFP_ZERO;
> > +
> > + if (in_atomic())
> > + gfp |= GFP_ATOMIC;
> > +
> > + return kmem_cache_alloc(dma_entry_cache, gfp);
>
> hm. that slab allocation in the middle of DMA mapping ops makes me a
> bit nervous. the DMA mapping ops are generally rather atomic.
>
> and in_atomic() check there is a bug on !PREEMPT kernels, so it wont
> fly.
I am not sure I understand this correctly. You say the check for
in_atomic() will break on !PREEMPT kernels?
> We dont have a gfp flag passed in as all the DMA mapping APIs really
> expect all allocations having been done in advance already.
Hmm, I can change the code to pre-allocate a certain (configurable?)
number of these entries and disble the checking if we run out of it.
> Any chance to attach the debug entry to the iotlb entries themselves -
> either during build time (for swiotlb) or during iommu init time (for
> the hw iommu's) ?
Hm, I want to avoid that. This approach has the advantage that is
works independent of any dma_ops implementation. So it can be used to
find out if a DMA bug originates from the device driver or (in my case)
from the IOMMU driver.
Joerg
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