From: Jie Chen <fykcee1@xxxxxxxxx>
Subject: lib/rbtree.c: fix typo in comment of ____rb_erase_color
In Case 3 of `sibling == parent->rb_right':
Right rotation will not change color of sl and S in the diagram
(i.e. should not change "sl" to "Sl", "S" to "s")
In Case 3 of `sibling == parent->rb_left':
(p) (p)
/ \ / \
S N --> sr N
/ \ /
Sl sr S
/
Sl
This is actually left rotation at "S", not right rotation.
In Case 4 of `sibling == parent->rb_left':
(p) (s)
/ \ / \
S N --> Sl P
/ \ / \
sl (sr) (sr) N
This is actually right rotation at "(p)" + color flips, not left
rotation + color flips.
Link: http://lkml.kernel.org/r/1472391115-3702-1-git-send-email-fykcee1@xxxxxxxxx
Signed-off-by: Jie Chen <fykcee1@xxxxxxxxx>
Cc: Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx>
Cc: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/rbtree.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff -puN lib/rbtree.c~lib-rbtreec-fix-typo-in-comment-of-____rb_erase_color lib/rbtree.c
--- a/lib/rbtree.c~lib-rbtreec-fix-typo-in-comment-of-____rb_erase_color
+++ a/lib/rbtree.c
@@ -296,11 +296,26 @@ ____rb_erase_color(struct rb_node *paren
*
* (p) (p)
* / \ / \
- * N S --> N Sl
+ * N S --> N sl
* / \ \
- * sl Sr s
+ * sl Sr S
* \
* Sr
+ *
+ * Note: p might be red, and then both
+ * p and sl are red after rotation(which
+ * breaks property 4). This is fixed in
+ * Case 4 (in __rb_rotate_set_parents()
+ * which set sl the color of p
+ * and set p RB_BLACK)
+ *
+ * (p) (sl)
+ * / \ / \
+ * N sl --> P S
+ * \ / \
+ * S N Sr
+ * \
+ * Sr
*/
tmp1 = tmp2->rb_right;
WRITE_ONCE(sibling->rb_left, tmp1);
@@ -365,7 +380,7 @@ ____rb_erase_color(struct rb_node *paren
}
break;
}
- /* Case 3 - right rotate at sibling */
+ /* Case 3 - left rotate at sibling */
tmp1 = tmp2->rb_left;
WRITE_ONCE(sibling->rb_right, tmp1);
WRITE_ONCE(tmp2->rb_left, sibling);
@@ -377,7 +392,7 @@ ____rb_erase_color(struct rb_node *paren
tmp1 = sibling;
sibling = tmp2;
}
- /* Case 4 - left rotate at parent + color flips */
+ /* Case 4 - right rotate at parent + color flips */
tmp2 = sibling->rb_right;
WRITE_ONCE(parent->rb_left, tmp2);
WRITE_ONCE(sibling->rb_right, parent);
_
--
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