Re: [PATCH 0/3] fix missing rb_subtree_gap updates on vma insert/erase

[Sasha Levin <levinsasha928@gmail.com>]

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.
> 
> These 3 patches apply on top of the stack I previously sent (or equally,
> on top of the last published mmotm).
> 
> Michel Lespinasse (3):
>   mm: ensure safe rb_subtree_gap update when inserting new VMA
>   mm: ensure safe rb_subtree_gap update when removing VMA
>   mm: debug code to verify rb_subtree_gap updates are safe
> 
>  mm/mmap.c |  121 +++++++++++++++++++++++++++++++++++++------------------------
>  1 files changed, 73 insertions(+), 48 deletions(-)
> 

Looking good: old warnings gone, no new warnings.


Thanks,
Sasha

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