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

[Johannes Weiner]

On Sat, Jan 14, 2017 at 07:57:51PM -0500, Johannes Weiner wrote:
> On Sat, Jan 14, 2017 at 09:31:51PM +0000, Matthew Wilcox wrote:
> > From: Johannes Weiner [mailto:hannes@xxxxxxxxxxx]
> > > 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@xxxxxxxxxxxxx>
> > > 
> > > 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.
> 
> Distinguishing between the radix_tree_shrink() and the delete_node()
> sites was essential to find the bug whose fix added these warnings.
> The former gets inlined into the latter. Not impossible to figure out
> which one triggered from a full dump, but certainly less robust.

This?