Messages in this thread | | | Date | Fri, 21 Nov 2008 18:10:04 +0100 | From | Joerg Roedel <> | Subject | Re: [PATCH 03/10] x86: add initialization code for DMA-API debugging |
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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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