Messages in this thread | | | Date | Tue, 11 Jan 2011 15:35:12 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH] mm: fix migration hangs on anon_vma lock |
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On 01/11/2011 02:08 AM, Hugh Dickins wrote: > Increased usage of page migration in mmotm reveals that the anon_vma > locking in unmap_and_move() has been deficient since 2.6.36 (or even > earlier). Review at the time of f18194275c39835cb84563500995e0d503a32d9a > "mm: fix hang on anon_vma->root->lock" missed the issue here: the anon_vma > to which we get a reference may already have been freed back to its slab > (it is in use when we check page_mapped, but that can change), and so its > anon_vma->root may be switched at any moment by reuse in anon_vma_prepare. > > Perhaps we could fix that with a get_anon_vma_unless_zero(), but let's not: > just rely on page_lock_anon_vma() to do all the hard thinking for us, then > we don't need any rcu read locking over here. > > In removing the rcu_unlock label: since PageAnon is a bit in page->mapping, > it's impossible for a !page->mapping page to be anon; but insert VM_BUG_ON > in case the implementation ever changes. > > Signed-off-by: Hugh Dickins<hughd@google.com> > Cc: stable@kernel.org [2.6.37, 2.6.36]
Reviewed-by: Rik van Riel <riel@redhat.com>
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