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lib: radix-tree: check accounting of existing slot replacement users

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The bug in khugepaged fixed earlier in this series shows that radix tree
slot replacement is fragile; and it will become more so when not only
NULL<->!NULL transitions need to be caught but transitions from and to
exceptional entries as well.  We need checks.

Re-implement radix_tree_replace_slot() on top of the sanity-checked
__radix_tree_replace().  This requires existing callers to also pass the
radix tree root, but it'll warn us when somebody replaces slots with
contents that need proper accounting (transitions between NULL entries,
real entries, exceptional entries) and where a replacement through the
slot pointer would corrupt the radix tree node counts.

Link: http://lkml.kernel.org/r/20161117193021.GB23430@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <mawilcox@linuxonhyperv.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2016-12-12 16:43:43 -08:00 • committed by Linus Torvalds
parent f7942430e4
commit 6d75f366b9
10 changed files with 64 additions and 40 deletions
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2
mm/truncate.c
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@ -49,7 +49,7 @@ static void clear_exceptional_entry(struct address_space *mapping,
goto unlock;
if (*slot != entry)
goto unlock;
radix_tree_replace_slot(slot, NULL);
radix_tree_replace_slot(&mapping->page_tree, slot, NULL);
mapping->nrexceptional--;
if (!node)
goto unlock;