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Commit ce093a04 authored by Jie Chen's avatar Jie Chen Committed by Linus Torvalds
Browse files

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@gmail.com


Signed-off-by: default avatarJie Chen <fykcee1@gmail.com>
Cc: Wei Yang <weiyang@linux.vnet.ibm.com>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6b2a65c7

lib/rbtree.c

+19 −4
Original line number Diff line number Diff line
@@ -296,9 +296,24 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, 
				 *

				 *   (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

				 */
@@ -365,7 +380,7 @@ ____rb_erase_color(struct rb_node *parent, struct rb_root *root, 
					}

					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 *parent, struct rb_root *root, 
				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);