lib: radix-tree: add radix_tree_delete_item()

Provide a function that does not just delete an entry at a given index,
but also allows passing in an expected item.  Delete only if that item
is still located at the specified index.

This is handy when lockless tree traversals want to delete entries as
well because they don't have to do an second, locked lookup to verify
the slot has not changed under them before deleting the entry.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Metin Doslu <metin@citusdata.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ozgun Erdogan <ozgun@citusdata.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <klamm@yandex-team.ru>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 403940787be18230a5201799d57020ed46177cab..1bf0a9c388d9fe9a1eba9e603a1f2732453067c9 100644 (file)
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -219,6 +219,7 @@ static inline void radix_tree_replace_slot(void **pslot, void *item)
 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
+void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 unsigned int
 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index bd4a8dfdf0b8052cdaedd0b3478eea4138ac100a..d832117e7d94942328690f4b275a5e10b3d6f9b4 100644 (file)
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -1337,15 +1337,18 @@ static inline void radix_tree_shrink(struct radix_tree_root *root)
 }
 
 /**
- *     radix_tree_delete    -    delete an item from a radix tree
+ *     radix_tree_delete_item    -    delete an item from a radix tree
  *     @root:          radix tree root
  *     @index:         index key
+ *     @item:          expected item
  *
- *     Remove the item at @index from the radix tree rooted at @root.
+ *     Remove @item at @index from the radix tree rooted at @root.
  *
- *     Returns the address of the deleted item, or NULL if it was not present.
+ *     Returns the address of the deleted item, or NULL if it was not present
+ *     or the entry at the given @index was not @item.
  */
-void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
+void *radix_tree_delete_item(struct radix_tree_root *root,
+                            unsigned long index, void *item)
 {
        struct radix_tree_node *node = NULL;
        struct radix_tree_node *slot = NULL;
@@ -1380,6 +1383,11 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
        if (slot == NULL)
                goto out;
 
+       if (item && slot != item) {
+               slot = NULL;
+               goto out;
+       }
+
        /*
         * Clear all tags associated with the item to be deleted.
         * This way of doing it would be inefficient, but seldom is any set.
@@ -1424,6 +1432,21 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 out:
        return slot;
 }
+EXPORT_SYMBOL(radix_tree_delete_item);
+
+/**
+ *     radix_tree_delete    -    delete an item from a radix tree
+ *     @root:          radix tree root
+ *     @index:         index key
+ *
+ *     Remove the item at @index from the radix tree rooted at @root.
+ *
+ *     Returns the address of the deleted item, or NULL if it was not present.
+ */
+void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
+{
+       return radix_tree_delete_item(root, index, NULL);
+}
 EXPORT_SYMBOL(radix_tree_delete);
 
 /**