rbtree: fix nil nodes handling

Don't copy and create new nodes for nil nodes. They have to always point to the
same!

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/urcu-rbtree.c b/urcu-rbtree.c
index 31f609fbcf838ab7e5cdf6ee4ab822cfe988f207..abe6de5cd1b3a0c9a2b72b768f06e72848ea18bc 100644 (file)
--- a/urcu-rbtree.c
+++ b/urcu-rbtree.c
@@ -157,16 +157,23 @@ static struct rcu_rbtree_node *left_rotate(struct rcu_rbtree_node **root,
 
        y = x->right;
 
-       yc = rballoc();
-       xc = rballoc();
-       *xc = *x;
-       *yc = *y;
-
-       /* Modify children and parents in the node copies */
-       xc->right = y->left;
-       xc->p = yc;
-       yc->left = xc;
-       yc->p = x->p;
+       if (x != &rcu_rbtree_nil) {
+               xc = rballoc();
+               *xc = *x;
+               /* Modify children and parents in the node copies */
+               xc->right = y->left;
+               xc->p = yc;
+       } else
+               xc = &rcu_rbtree_nil;
+
+       if (y != &rcu_rbtree_nil) {
+               yc = rballoc();
+               *yc = *y;
+               /* Modify children and parents in the node copies */
+               yc->left = xc;
+               yc->p = x->p;
+       } else
+               yc = &rcu_rbtree_nil;
 
        /*
         * Order stores to node copies (children/parents) before stores that
@@ -183,13 +190,16 @@ static struct rcu_rbtree_node *left_rotate(struct rcu_rbtree_node **root,
                _STORE_SHARED(x->p->right, yc);
 
        /* Assign children parents to copies */
-       _STORE_SHARED(xc->right->p, xc);
-       _STORE_SHARED(xc->left->p, xc);
-       _STORE_SHARED(yc->right->p, yc);
-       /* yc->left is xc, its parent is already set in node copy */
-
-       defer_rcu(rbfree, x);
-       defer_rcu(rbfree, y);
+       if (x != &rcu_rbtree_nil) {
+               _STORE_SHARED(xc->right->p, xc);
+               _STORE_SHARED(xc->left->p, xc);
+               defer_rcu(rbfree, x);
+       }
+       if (y != &rcu_rbtree_nil) {
+               _STORE_SHARED(yc->right->p, yc);
+               defer_rcu(rbfree, y);
+               /* yc->left is xc, its parent is already set in node copy */
+       }
        return xc;
 }
 
@@ -228,16 +238,23 @@ static struct rcu_rbtree_node *right_rotate(struct rcu_rbtree_node **root,
 
        y = x->left;
 
-       yc = rballoc();
-       xc = rballoc();
-       *xc = *x;
-       *yc = *y;
-
-       /* Modify children and parents in the node copies */
-       xc->left = y->right;
-       xc->p = yc;
-       yc->right = xc;
-       yc->p = x->p;
+       if (x != &rcu_rbtree_nil) {
+               xc = rballoc();
+               *xc = *x;
+               /* Modify children and parents in the node copies */
+               xc->left = y->right;
+               xc->p = yc;
+       } else
+               xc = &rcu_rbtree_nil;
+
+       if (y != &rcu_rbtree_nil) {
+               yc = rballoc();
+               *yc = *y;
+               /* Modify children and parents in the node copies */
+               yc->right = xc;
+               yc->p = x->p;
+       } else
+               yc = &rcu_rbtree_nil;
 
        /*
         * Order stores to node copies (children/parents) before stores that
@@ -254,13 +271,16 @@ static struct rcu_rbtree_node *right_rotate(struct rcu_rbtree_node **root,
                _STORE_SHARED(x->p->left, yc);
 
        /* Assign children parents to copies */
-       _STORE_SHARED(xc->left->p, xc);
-       _STORE_SHARED(xc->right->p, xc);
-       _STORE_SHARED(yc->left->p, yc);
-       /* yc->right is xc, its parent is already set in node copy */
-
-       defer_rcu(rbfree, x);
-       defer_rcu(rbfree, y);
+       if (x != &rcu_rbtree_nil) {
+               _STORE_SHARED(xc->left->p, xc);
+               _STORE_SHARED(xc->right->p, xc);
+               defer_rcu(rbfree, x);
+       }
+       if (y != &rcu_rbtree_nil) {
+               _STORE_SHARED(yc->left->p, yc);
+               defer_rcu(rbfree, y);
+               /* yc->right is xc, its parent is already set in node copy */
+       }
        return xc;
 }
 
@@ -399,17 +419,21 @@ rcu_rbtree_transplant(struct rcu_rbtree_node **root,
 {
        struct rcu_rbtree_node *vc;
 
-       vc = rballoc();
-       *vc = *v;
+       if (v != &rcu_rbtree_nil) {
+               vc = rballoc();
+               *vc = *v;
 
-       /* Change vc parent pointer */
-       vc->p = u->p;
+               /* Change vc parent pointer */
+               vc->p = u->p;
 
-       /*
-        * Order stores to node copies (children/parents) before stores that
-        * will make the copies visible to the rest of the tree.
-        */
-       smp_wmb();
+               /*
+                * Order stores to node copies (children/parents) before stores
+                * that will make the copies visible to the rest of the tree.
+                */
+               smp_wmb();
+       } else {
+               vc = &rcu_rbtree_nil;
+       }
 
        /* Assign upper-level pointer to vc, replacing u. */
        if (u->p == &rcu_rbtree_nil)
@@ -419,14 +443,16 @@ rcu_rbtree_transplant(struct rcu_rbtree_node **root,
        else
                _STORE_SHARED(u->p->right, vc);
 
-       /*
-        * The children pointers in vc are the same as v. We can therefore
-        * reparent v's children to vc safely.
-        */
-       _STORE_SHARED(vc->right->p, vc);
-       _STORE_SHARED(vc->left->p, vc);
+       if (v != &rcu_rbtree_nil) {
+               /*
+                * The children pointers in vc are the same as v. We can
+                * therefore reparent v's children to vc safely.
+                */
+               _STORE_SHARED(vc->right->p, vc);
+               _STORE_SHARED(vc->left->p, vc);
 
-       defer_rcu(rbfree, v);
+               defer_rcu(rbfree, v);
+       }
        return vc;
 }