Messages in this thread | | | Date | Sun, 11 Apr 2010 17:13:26 -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 Sun, 11 Apr 2010, Borislav Petkov wrote: > > > Conversely, if you still see the oops (rather than the watchdog), that > > means that we actually have pages that are still marked mapped, and that > > despite that mapped state have a stale page->mapping pointer. I actually > > find that the more likely case, because otherwise the window is _so_ small > > that I don't see how you can hit the oops so reliably. > > Ok, did test with the all 5 patches applied. It oopsed with the same > trace, see below. Except one kernel/sched.c:3555 warning checking > spinlock count overflowing, nothing else. :(
Ok, that preempt-count thing is a real problem, but should be unrelated to your issues.
Anyway, so this all means that we definitely have lost sight of an 'anon_vma', even if page->mapping still points to it, and even though the page is still mapped.
I'll see if I can come up with a patch to do the same kind of validation on page->mapping as on the anon-vma chains themselves.
> I tried to see whether the page->mapping pointer is stale, I dunno, > maybe there could be something in the register dump which could tell us > what's happening.
Sadly, you cannot tell by the pointer. A stale pointer still is a perfectly fine kernel pointer, it's just that we've long since released the anon_vma it used to point to, and now it points to some random other data structure.
> So, it really looks like at least that list_head in anon_vma is > bollocks, or even the whole anon_vma. So if this is correct, it is > highly likely that the anon_vma is already freed material or not > initialized at all.
Yes, it's pretty certain it is long free'd, and re-allocated to something else.
Linus
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