Messages in this thread | | | Date | Mon, 12 Nov 2012 08:39:59 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH 1/3] mm: ensure safe rb_subtree_gap update when inserting new VMA |
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On 11/12/2012 06:51 AM, Michel Lespinasse wrote: > Using the trinity fuzzer, Sasha Levin uncovered a case where > rb_subtree_gap wasn't correctly updated. > > Digging into this, the root cause was that vma insertions and removals > require both an rbtree insert or erase operation (which may trigger > tree rotations), and an update of the next vma's gap (which does not > change the tree topology, but may require iterating on the node's > ancestors to propagate the update). The rbtree rotations caused the > rb_subtree_gap values to be updated in some of the internal nodes, but > without upstream propagation. Then the subsequent update on the next > vma didn't iterate as high up the tree as it should have, as it > stopped as soon as it hit one of the internal nodes that had been > updated as part of a tree rotation. > > The fix is to impose that all rb_subtree_gap values must be up to date > before any rbtree insertion or erase, with the possible exception that > the node being erased doesn't need to have an up to date rb_subtree_gap. > > This change: during vma insertion, make sure to update the rb_subtree_gap > values for both the current and next vmas prior to rebalancing the rbtree > to account for the just-inserted vma. > > (Thanks to Sasha Levin for uncovering the problem and to Hugh Dickins > for coming up with a simpler test case) > > Reported-by: Sasha Levin <sasha.levin@oracle.com> > Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
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