Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
authored by
Peter Zijlstra
and committed by
Linus Torvalds
bc658c96
139f37f5
+6
-1
+6
-1
mm/rmap.c
+6
-1
mm/rmap.c
···
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* The page might have been remapped to a different anon_vma or the anon_vma
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* returned may already be freed (and even reused).
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*
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* In case it was remapped to a different anon_vma, the new anon_vma will be a
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* child of the old anon_vma, and the anon_vma lifetime rules will therefore
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* ensure that any anon_vma obtained from the page will still be valid for as
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* long as we observe page_mapped() [ hence all those page_mapped() tests ].
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*
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* All users of this function must be very careful when walking the anon_vma
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* chain and verify that the page in question is indeed mapped in it
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* [ something equivalent to page_mapped_in_vma() ].
···
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/*
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* If the page is still mapped, then this anon_vma is still
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* its anon_vma, and holding the mutex ensures that it will
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* not go away, see __put_anon_vma().
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* not go away, see anon_vma_free().
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*/
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if (!page_mapped(page)) {
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mutex_unlock(&root_anon_vma->mutex);