Messages in this thread | | | Date | Mon, 12 Nov 2012 08:40:17 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH 2/3] mm: ensure safe rb_subtree_gap update when removing VMA |
| |
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 removal, remove VMA from the rbtree before we > remove it from the linked list. The implication is the next vma's > rb_subtree_gap value becomes stale when next->vm_prev is updated, > and we want to make sure vma_rb_erase() runs before there are any > such stale rb_subtree_gap values in the rbtree. > > (I don't know of a reproduceable test case for this particular issue) > > Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
-- All rights reversed
| |