On Fri, Jun 05, 2009 at 05:52:27PM +0200, Torsten Kaiser wrote: > > This doesn't look right to me. > The comment above says "returns the entry from the hash which fits > best", but this will always return NULL, if there are are multiple > entrys, but no perfect match. This is intentional. If there is no perfect-fit there is no way to tell which entry was meant. So we potentially report wrong errors with a wrong mapping backtrace which confuses even more than the wrong "DMA-API: device driver tries to free DMA memory it has not allocated". > 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. > * driver wants to correctly unmap the first allocation > -> wrong warning about this unmap because size mismatch Ok, at least we get a warning about a bug. Not very useful because it reports the wrong bug. Is this the situation which triggered the original bug report? > Also what about sg_call_ents and sg_mapped_ents? > Could it be possible to get the same address/size with different sg-counts. It looks not forbidden in the API. So I guess this can happen too. Regards, Joerg -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
