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SubjectRe: [PATCH] dma-debug: disable DMA_API_DEBUG for now
On Fri, Jun 5, 2009 at 8:20 PM, Joerg Roedel <> wrote:
> On Fri, Jun 05, 2009 at 05:52:27PM +0200, Torsten Kaiser wrote:
>> Should there be a warning if more then one possible match were found?
> True. That would be better. But I tried to keep the code change as small
> as possible without disabling the feature completly.
>> * driver maps address 'a' with size 1
>> * driver maps same address 'a' with size 2
>> * driver wrongly unmaps the second allocation with size 1
>> -> no warning, because the first allocation is returned
> Hmm, I am not sure if we can handle this situation correctly in the
> dma-debug code. There is no unique key to identify a mapping request
> which allows to assign an unmap request to it. Currently dma-debug uses
> device and dma-address. But that seems not to be sufficient. The
> best-fit algorithm is also a but fuzzy of course.

Maybe we just shouldn't try to handle it at all:

static void add_dma_entry(struct dma_debug_entry *entry)
struct hash_bucket *bucket;
unsigned long flags;

bucket = get_hash_bucket(entry, &flags);
if(hash_bucket_find(bucket, entry)) {
printk(KERN_ERR "DMA-API: device mapped same address twice, "
"this use case cannot be handled currently -
disabling debugging\n");
global_disable = true;
hash_bucket_add(bucket, entry);
put_hash_bucket(bucket, &flags);

This would allow this feature to remain for most cased, but would also
prevent all false warnings.


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