RE: [PATCH] radix-tree: Fix private list warnings

Matthew Wilcox
2017-01-14T21:31:55Z

From: Johannes Weiner [mailto:hannes@cmpxchg.org]
> On Thu, Jan 12, 2017 at 05:28:23PM -0800, Matthew Wilcox wrote:
> > The newly introduced warning in radix_tree_free_nodes() was testing the
> > wrong variable; it should have been 'old' instead of 'node'. Rather
> > than replace that one instance, I noticed that we can simply put the
> > WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
> >
> > Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node
> shrinker")
> > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
>
> Thanks for the fix in radix_tree_free_nodes(). But I intentionally
> spread out the warnings to retain the line numbers. The inlining in
> that code will obscure which tree operation ends up triggering.

The backtrace should make that fairly obvious though; even if radix_tree_node_free() gets inlined, the caller of radix_tree_free_nodes() probably doesn't also call radix_tree_shrink() or delete_node(). You're really looking for the caller in the backtrace that's outside of radix-tree.c.

By the way, if you'd run the radix tree test-suite, the WARN_ON_ONCE would have triggered (that's how I spotted the bug). The test-suite is getting pretty useful these days; would you mind running it in future?