[Xen-changelog] [xen master] rbtree: break out of rb_insert_color loop after tree rotation

[patchbot@xxxxxxx]

commit 344824c0f4b6aae3deca1e8b15d4e3f26a761682
Author:     Michel Lespinasse <walken@xxxxxxxxxx>
AuthorDate: Wed Dec 20 18:02:12 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Dec 20 18:02:12 2017 +0100

    rbtree: break out of rb_insert_color loop after tree rotation
    
    It is a well known property of rbtrees that insertion never requires more
    than two tree rotations.  In our implementation, after one loop iteration
    identified one or two necessary tree rotations, we would iterate and look
    for more.  However at that point the node's parent would always be black,
    which would cause us to exit the loop.
    
    We can make the code flow more obvious by just adding a break statement
    after the tree rotations, where we know we are done.  Additionally, in the
    cases where two tree rotations are necessary, we don't have to update the
    'node' pointer as it wouldn't be used until the next loop iteration, which
    we now avoid due to this break statement.
    
    Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
    Acked-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
    [Linux commit 1f0528653e41ec230c60f5738820e8a544731399]
    
    Ported to Xen.
    
    Signed-off-by: Praveen Kumar <kpraveen.lkml@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/rbtree.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index a75b336..9dc296e 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -109,18 +109,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root 
*root)
                                }
                        }
 
-                       if (parent->rb_right == node)
-                       {
-                               register struct rb_node *tmp;
+                       if (parent->rb_right == node) {
                                __rb_rotate_left(parent, root);
-                               tmp = parent;
                                parent = node;
-                               node = tmp;
                        }
 
                        rb_set_black(parent);
                        rb_set_red(gparent);
                        __rb_rotate_right(gparent, root);
+                       break;
                } else {
                        {
                                register struct rb_node *uncle = 
gparent->rb_left;
@@ -134,18 +131,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root 
*root)
                                }
                        }
 
-                       if (parent->rb_left == node)
-                       {
-                               register struct rb_node *tmp;
+                       if (parent->rb_left == node) {
                                __rb_rotate_right(parent, root);
-                               tmp = parent;
                                parent = node;
-                               node = tmp;
                        }
 
                        rb_set_black(parent);
                        rb_set_red(gparent);
                        __rb_rotate_left(gparent, root);
+                       break;
                }
        }
 
--
generated by git-patchbot for /home/xen/git/xen.git#master

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