On Sat, Jan 14, 2017 at 09:31:51PM +0000, Matthew Wilcox wrote: > From: Johannes Weiner [mailto:[email protected]] > > 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 <[email protected]> > > > > 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. > 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? Thanks, I'll keep that in mind for future radix tree changes.
