Messages in this thread | | | Date | Fri, 9 Apr 2010 09:35:15 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas of a mergeable VMA |
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On Fri, 9 Apr 2010, Borislav Petkov wrote: > > So I went and reapplied the three patches (3rd is the object_err export > for SLUB debugging) on a new branch of today's git - same results, the > same processes crap up in the WARN(!vma->anon_vma) check so it should be > something else we're missing. > > More code staring later...
Can you try with _just_ my patch? Or add a
vma->anon_vma = merge_vma->anon_vma;
to Rik's "merge_vma" case in anon_vma_prepare().
Because I'm starign at Rik's patch, and one thing strikes me: it does that "anon_vma_clone()" in anon_vma_prepare(), and maybe I'm blind, but I don't see where that actually sets vma->anon_vma.
As far as I can tell, anon_vma_clone() was designed purely for the fork() case, which has done
*new = *vma;
which will set new->anon_vma to the same vma. But Rik's patch never does that for the anon_vma_prepare() case.
And maybe we should do it in anon_vma_clone() itself, just to make it impossible to mistakenly leave it out, the way I think Rik's patch did.
Anyway, I'm still groggy from allt he flu medication, so take everything I say with a grain of salt.
In fact, the more I look at this, the less I think I like Rik's patch in the first place. I think the real bug that Rik tried to fix is that apparently anon_vma_merge() doesn't necessarily merge everything right. From Rik's bug-explanation, step 5:
>> 5) vma_adjust calls anon_vma_merge, causing the anon_vma >> chain of one of the VMAs to get nuked - with bad luck, >> this is the original one, leaving just the new anon_vma >> attached to the VMA
and I think that _this_ is the real bug to begin with. The real fix should be in vma_adjust/anon_vma_merge, not in how we set up the anon_vma in the first place. I do _not_ think we should require that we always merged things at mmap() time, because we may _never_ be able to merge perfectly (ie start out with to disjoing mmaps, and fill in the middle).
Linus
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