path: root/lib
diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2016-09-25 13:32:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-25 13:32:46 -0700
commit8d2c0d36d6826ddc3114801c599619d3f2932f0a (patch)
tree826496294c0a46b6f66a65584e01ec6fe70278bf /lib
parent62fd5258ebe3ea240371234955a6e2cc99e0b6c3 (diff)
radix tree: fix sibling entry handling in radix_tree_descend()
The fixes to the radix tree test suite show that the multi-order case is broken. The basic reason is that the radix tree code uses tagged pointers with the "internal" bit in the low bits, and calculating the pointer indices was supposed to mask off those bits. But gcc will notice that we then use the index to re-create the pointer, and will avoid doing the arithmetic and use the tagged pointer directly. This cleans the code up, using the existing is_sibling_entry() helper to validate the sibling pointer range (instead of open-coding it), and using entry_to_node() to mask off the low tag bit from the pointer. And once you do that, you might as well just use the now cleaned-up pointer directly. [ Side note: the multi-order code isn't actually ever used in the kernel right now, and the only reason I didn't just delete all that code is that Kirill Shutemov piped up and said: "Well, my ext4-with-huge-pages patchset[1] uses multi-order entries. It also converts shmem-with-huge-pages and hugetlb to them. I'm okay with converting it to other mechanism, but I need something. (I looked into Konstantin's RFC patchset[2]. It looks okay, but I don't feel myself qualified to review it as I don't know much about radix-tree internals.)" [1] http://lkml.kernel.org/r/20160915115523.29737-1-kirill.shutemov@linux.intel.com [2] http://lkml.kernel.org/r/147230727479.9957.1087787722571077339.stgit@zurg ] Reported-by: Matthew Wilcox <mawilcox@microsoft.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Cedric Blancher <cedric.blancher@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
1 files changed, 4 insertions, 4 deletions
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1b7bf7314141..91f0727e3cad 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -105,10 +105,10 @@ static unsigned int radix_tree_descend(struct radix_tree_node *parent,
if (radix_tree_is_internal_node(entry)) {
- unsigned long siboff = get_slot_offset(parent, entry);
- if (siboff < RADIX_TREE_MAP_SIZE) {
- offset = siboff;
- entry = rcu_dereference_raw(parent->slots[offset]);
+ if (is_sibling_entry(parent, entry)) {
+ void **sibentry = (void **) entry_to_node(entry);
+ offset = get_slot_offset(parent, sibentry);
+ entry = rcu_dereference_raw(*sibentry);