Messages in this thread | | | Date | Sun, 16 Mar 2008 20:55:03 +0900 | Subject | Re: [PATCH] avoid endless loops in lib/swiotlb.c | From | FUJITA Tomonori <> |
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On Fri, 14 Mar 2008 10:18:09 +0000 "Jan Beulich" <jbeulich@novell.com> wrote:
> >> - if the number of slots requested fits into a swiotlb segment, but is > >> too large for the part of a segment which remains after considering > >> offset_slots > > > >Sorry, I'm not sure what you mean. Can you give me an actual example > >numbers that leads to that? > > For one part, it can happen if nslots > max_slots (which is a driver > error [except for the case above where max_slots erroneously got set > to zero], but shouldn't lead to a silent hang, especially as it didn't do so > before). > > For another part, requesting e.g. a transfer of 128k with a segment > mask of 128k when the IOTLB isn't aligned to a 128k boundary would > again lead to a silent hang, as would various cases where the request > exceeds the segment size (and the segment mask is sufficiently small). > Neither of these cases got stuck in the old code. > > Beyond that, maybe I was too quick in concluding this could happen > even in less unusual cases - I think I didn't pay close enough attention > to the fact that offset_slots + index gets masked by max_slots - 1. > But even then I think the code looks simpler/safer and is smaller with > the adjusted logic.
I don't think that the old code hits the problems (endless loops or silent hang) that you explained, but I agree that the patch made the code simpler a bit.
Thanks,
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