On Sun, Sep 25, 2016 at 11:04 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> The more I look at that particular piece of code, the less I like it. It's
> buggy shit. It needs to be rewritten entirely too actually check for sibling
> entries, not that ad-hoc arithmetic crap.
Here's my attempt at cleaning the mess up.
I'm not claiming it's perfect, but I think it's better. It gets rid of
the ad-hoc arithmetic in radix_tree_descend(), and just makes all that
be inside the is_sibling_entry() logic instead. Which got renamed and
made to actually return the main sibling. So now there is at least
only *one* piece of code that does that range comparison, and I don't
think there is any huge need to explain what's going on, because the
"magic" is unconditional.
Willy?
Linus
lib/radix-tree.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1b7bf7314141..210709b07759 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -78,18 +78,20 @@ static inline void *node_to_entry(void *ptr)
#ifdef CONFIG_RADIX_TREE_MULTIORDER
/* Sibling slots point directly to another slot in the same node */
-static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
+static inline void **get_sibling_entry(struct radix_tree_node *parent, void *node)
{
- void **ptr = node;
- return (parent->slots <= ptr) &&
- (ptr < parent->slots + RADIX_TREE_MAP_SIZE);
+ void **ptr = (void **) entry_to_node(node);
+ if ((parent->slots <= ptr) && (ptr < parent->slots + RADIX_TREE_MAP_SIZE))
+ return ptr;
+ return NULL;
}
#else
-static inline bool is_sibling_entry(struct radix_tree_node *parent, void *node)
+static inline void **get_sibling_entry(struct radix_tree_node *parent, void *node)
{
- return false;
+ return NULL;
}
#endif
+#define is_sibling_entry(parent, node) (get_sibling_entry(parent,node) != NULL)
static inline unsigned long get_slot_offset(struct radix_tree_node *parent,
void **slot)
@@ -105,10 +107,10 @@ static unsigned int radix_tree_descend(struct radix_tree_node *parent,
#ifdef CONFIG_RADIX_TREE_MULTIORDER
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]);
+ void **sibentry = get_sibling_entry(parent, entry);
+ if (sibentry) {
+ offset = get_slot_offset(parent, sibentry);
+ entry = rcu_dereference_raw(*sibentry);
}
}
#endif
