Messages in this thread | | | Date | Fri, 10 Apr 2015 10:56:07 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [Question] ksm: rmap_item pointing to some stale vmas |
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On Thu, 9 Apr 2015, Susheel Khiani wrote:
> Hi, > > We are seeing an issue during try_to_unmap_ksm where in call to > try_to_unmap_one is failing. > > try_to_unmap_ksm in this particular case is trying to go through vmas > associated with each rmap_item->anon_vma. What we see is this that the > corresponding page is not mapped to any of the vmas associated with 2 > rmap_item. > > The associated rmap_item in this case looks like pointing to some valid vma > but the said page is not found to be mapped under it. try_to_unmap_one thus > fails to find valid ptes for these vmas. > > At the same time we can see that the page actually is mapped in 2 separate > and different vmas which are not part of rmap_item associated with page. > > So whether rmap_item is pointing to some stale vmas and now the mapping has > changed? Or there is something else going on here. > p > Any pointer would be appreciated.
I expected to be able to argue this away, but no: I think you've found a bug, and I think I get it too. I have no idea what's wrong at this point, will set aside some time to investigate, and report back.
Which kernel are you using? try_to_unmap_ksm says v3.13 or earlier. Probably doesn't affect the bug, but may affect the patch you'll need.
Hugh
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