Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page()

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From	"Kirill A. Shutemov" <kirill@shutemov.name>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page()
Date	Mon, 01 Feb 2016 15:40:02 +0100
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On Mon, Feb 01, 2016 at 03:24:46PM +0100, Michal Hocko wrote:
> On Mon 01-02-16 16:26:08, Kirill A. Shutemov wrote:
> > We don't care if there's a tail pages which is not on LRU. We are not
> > going to isolate them anyway.
> 
> yes we are not going to isolate them but calling this function on a
> tail page is wrong in principle, no? PageLRU check is racy outside of
> lru_lock so what if we are racing here. I know, highly unlikely but not
> impossible. So I am not really sure this is an improvement. When would
> we hit this VM_BUG_ON and it wouldn't be a bug or at least suspicious
> usage?

Yes, there is no point in calling isolate_lru_page() for tail pages, but
we do this anyway -- see the second patch.

And we need to validate all drivers, that they don't forget to set VM_IO
or make vma_migratable() return false in other way.

Alternative approach would be to downgrate the VM_BUG_ON_PAGE() to
WARN_ONCE_ON(). This way we would have chance to catch bad callers.

-- 
 Kirill A. Shutemov

Thread

[PATCH 0/2] Fix another VM_BUG_ON_PAGE(PageTail(page)) on mbind(2) "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-01 14:30 +0100
  [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-01 14:30 +0100
    Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page() Michal Hocko <mhocko@kernel.org> - 2016-02-01 15:30 +0100
      Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page() "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-01 15:40 +0100
        Re: [PATCH 1/2] mm: fix bogus VM_BUG_ON_PAGE() in isolate_lru_page() Michal Hocko <mhocko@kernel.org> - 2016-02-02 14:30 +0100
  [PATCH 2/2] mempolicy: do not try to queue pages from !vma_migratable() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-01 14:30 +0100
    Re: [PATCH 2/2] mempolicy: do not try to queue pages from  !vma_migratable() Andrew Morton <akpm@linux-foundation.org> - 2016-02-01 23:30 +0100

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