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mm, rmap: Add yet more comments to page_get_anon_vma/page_lock_anon_vma

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Inspired by an analysis from Hugh on why again all this doesn't explode
in our face.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra
2011-05-29 10:33:44 +02:00
committed by Linus Torvalds
parent 139f37f5e1
commit bc658c9603
1 changed files with 6 additions and 1 deletions
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7
mm/rmap.c
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@@ -352,6 +352,11 @@ void __init anon_vma_init(void)
* The page might have been remapped to a different anon_vma or the anon_vma * The page might have been remapped to a different anon_vma or the anon_vma
* returned may already be freed (and even reused). * returned may already be freed (and even reused).
* *
* In case it was remapped to a different anon_vma, the new anon_vma will be a
* child of the old anon_vma, and the anon_vma lifetime rules will therefore
* ensure that any anon_vma obtained from the page will still be valid for as
* long as we observe page_mapped() [ hence all those page_mapped() tests ].
*
* All users of this function must be very careful when walking the anon_vma * All users of this function must be very careful when walking the anon_vma
* chain and verify that the page in question is indeed mapped in it * chain and verify that the page in question is indeed mapped in it
* [ something equivalent to page_mapped_in_vma() ]. * [ something equivalent to page_mapped_in_vma() ].
@@ -421,7 +426,7 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
/* /*
* If the page is still mapped, then this anon_vma is still * If the page is still mapped, then this anon_vma is still
* its anon_vma, and holding the mutex ensures that it will * its anon_vma, and holding the mutex ensures that it will
* not go away, see __put_anon_vma(). * not go away, see anon_vma_free().
*/ */
if (!page_mapped(page)) { if (!page_mapped(page)) {
mutex_unlock(&root_anon_vma->mutex); mutex_unlock(&root_anon_vma->mutex);