Messages in this thread | | | Date | Mon, 22 May 2006 11:11:36 -0700 | From | "Randy.Dunlap" <> | Subject | Re: [PATCH] kmap tracking |
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On Mon, 22 May 2006 10:58:54 -0700 Zach Brown wrote:
> > > I was scratching my head over this patch trying to think of any bug in > > recent years which it would have detected. I failed. > > 2.4 nfs used to require that it be able to kmap entire RPCs for them to > make forward progress. Its file->write() required RPC forward progress > before it would return. And some callers were holding kmaps across > file->write() calls. So with enough concurrent callers doing that the > system would get stuck. > > We used the patch to see who the callers were when the system got into > that state. > > One of them was core dumping, believe it or not. 2.6 elf_core_dump() > still holds a kmap across file->write(), which seems unwise, but I > haven't gotten to seeing if it's worth worrying about or not. > > So maybe these days the kmap story is less dreadful and it isn't as > helpful, but that's what we used it for.
I was planning to add kmap_atomic* variants to the patch. I could see it being useful for those callers, but maybe problems with them would be more obvious anyway and wouldn't need such a patch.
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