Messages in this thread | | | Date | Mon, 22 May 2006 10:58:54 -0700 | From | Zach Brown <> | Subject | Re: [PATCH] kmap tracking |
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> 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.
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