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Commit bc658c96 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
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mm, rmap: Add yet more comments to page_get_anon_vma/page_lock_anon_vma



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

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 139f37f5
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+6 −1
Original line number Diff line number Diff line
@@ -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
 * 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
 * chain and verify that the page in question is indeed mapped in it
 * [ 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
		 * 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)) {
			mutex_unlock(&root_anon_vma->mutex);