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core/rbtree: make clear distinction between two different cases in rb_erase() 

See kernel commit 4c60117811171d867d4f27f17ea07d7419d45dae

----
There are two cases when a node, having 2 childs, is erased:
'normal case': the successor is not the right-hand-child of the node to be erased
'special case': the successor is the right-hand child of the node to be erased

Here some ascii-art, with following symbols (referring to the code):
O: node to be deleted
N: the successor of O
P: parent of N
C: child of N
L: some other node

normal case:

               O                         N
              / \                       / \
             /   \                     /   \
            L     \                   L     \
           / \     P      ---->      / \     P
                  / \                       / \
                 /                         /
                N                         C
                 \                       / \
                  \
                   C
                  / \

special case:
              O|P                        N
              / \                       / \
             /   \                     /   \
            L     \                   L     \
           / \     N      ---->      /       C
                    \                       / \
                     \
                      C
                     / \

Notice that for the special case we don't have to reconnect C to N.

Signed-off-by: Wolfram Strepp <wstrepp@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
----

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
This commit is contained in:
Sylvain Munaut 2011-11-11 15:29:59 +01:00 committed by Harald Welte
parent b8c5bdefcd
commit a83cbe12f8
1 changed files with 4 additions and 4 deletions
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8
src/rbtree.c
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@ -242,13 +242,13 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
parent = rb_parent(node);
color = rb_color(node);
if (child)
rb_set_parent(child, parent);
if (parent == old) {
parent->rb_right = child;
parent = node;
} else
} else {
if (child)
rb_set_parent(child, parent);
parent->rb_left = child;
}
node->rb_parent_color = old->rb_parent_color;
node->rb_right = old->rb_right;