Messages in this thread | | | Date | Thu, 5 May 2016 17:24:06 +0200 | From | Andrea Arcangeli <> | Subject | Re: [BUG] vfio device assignment regression with THP ref counting redesign |
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On Thu, May 05, 2016 at 06:11:10PM +0300, Kirill A. Shutemov wrote: > Hm. How total_mapcount equal to NULL wouldn't lead to NULL-pointer > dereference inside page_trans_huge_mapcount()?
Sorry for the confusion, this was still work in progress and then I've seen the email from Alex and I sent the last version I had committed right away. An earlier version of course had the proper checks for NULL but they got wiped as I transitioned from one model to another and back.
> > + page_move_anon_rmap(old_page, vma, address); > > compound_head() is missing, I believe.
Oh yes, fixed that too.
if (total_mapcount == 1) { /* * The page is all ours. Move it to * our anon_vma so the rmap code will * not search our parent or siblings. * Protected against the rmap code by * the page lock. */ page_move_anon_rmap(compound_head(old_page), vma, address); }
If there's no other issue I can git send-email.
Then we should look into calling page_move_anon_rmap from THP COWs too, hugetlbfs calls it too. I think we probably need to make page_move_anon_rmap smarter and optionally let it take the lock for us after reading page->mapping first to be sure it's really moving it.
The question is then if trylock or lock_page should be used, my preference would be just trylock.
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