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267 lines
8.1 KiB
267 lines
8.1 KiB
From: Alexander Duyck <alexander.h.duyck@redhat.com>
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Date: Thu, 22 Jan 2015 15:51:14 -0800
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Subject: [PATCH] fib_trie: Fix RCU bug and merge similar bits of inflate/halve
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This patch addresses two issues.
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The first issue is the fact that I believe I had the RCU freeing sequence
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slightly out of order. As a result we could get into an issue if a caller
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went into a child of a child of the new node, then backtraced into the to be
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freed parent, and then attempted to access a child of a child that may have
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been consumed in a resize of one of the new nodes children. To resolve this I
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have moved the resize after we have freed the oldtnode. The only side effect
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of this is that we will now be calling resize on more nodes in the case of
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inflate due to the fact that we don't have a good way to test to see if a
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full_tnode on the new node was there before or after the allocation. This
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should have minimal impact however since the node should already be
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correctly size so it is just the cost of calling should_inflate that we
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will be taking on the node which is only a couple of cycles.
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The second issue is the fact that inflate and halve were essentially doing
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the same thing after the new node was added to the trie replacing the old
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one. As such it wasn't really necessary to keep the code in both functions
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so I have split it out into two other functions, called replace and
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update_children.
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Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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--- a/net/ipv4/fib_trie.c
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+++ b/net/ipv4/fib_trie.c
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@@ -396,8 +396,30 @@ static void put_child(struct tnode *tn,
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rcu_assign_pointer(tn->child[i], n);
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}
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-static void put_child_root(struct tnode *tp, struct trie *t,
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- t_key key, struct tnode *n)
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+static void update_children(struct tnode *tn)
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+{
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+ unsigned long i;
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+
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+ /* update all of the child parent pointers */
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+ for (i = tnode_child_length(tn); i;) {
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+ struct tnode *inode = tnode_get_child(tn, --i);
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+
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+ if (!inode)
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+ continue;
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+
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+ /* Either update the children of a tnode that
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+ * already belongs to us or update the child
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+ * to point to ourselves.
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+ */
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+ if (node_parent(inode) == tn)
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+ update_children(inode);
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+ else
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+ node_set_parent(inode, tn);
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+ }
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+}
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+
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+static inline void put_child_root(struct tnode *tp, struct trie *t,
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+ t_key key, struct tnode *n)
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{
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if (tp)
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put_child(tp, get_index(key, tp), n);
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@@ -434,10 +456,35 @@ static void tnode_free(struct tnode *tn)
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}
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}
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+static void replace(struct trie *t, struct tnode *oldtnode, struct tnode *tn)
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+{
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+ struct tnode *tp = node_parent(oldtnode);
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+ unsigned long i;
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+
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+ /* setup the parent pointer out of and back into this node */
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+ NODE_INIT_PARENT(tn, tp);
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+ put_child_root(tp, t, tn->key, tn);
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+
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+ /* update all of the child parent pointers */
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+ update_children(tn);
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+
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+ /* all pointers should be clean so we are done */
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+ tnode_free(oldtnode);
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+
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+ /* resize children now that oldtnode is freed */
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+ for (i = tnode_child_length(tn); i;) {
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+ struct tnode *inode = tnode_get_child(tn, --i);
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+
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+ /* resize child node */
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+ if (tnode_full(tn, inode))
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+ resize(t, inode);
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+ }
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+}
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+
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static int inflate(struct trie *t, struct tnode *oldtnode)
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{
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- struct tnode *inode, *node0, *node1, *tn, *tp;
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- unsigned long i, j, k;
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+ struct tnode *tn;
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+ unsigned long i;
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t_key m;
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pr_debug("In inflate\n");
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@@ -446,13 +493,18 @@ static int inflate(struct trie *t, struc
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if (!tn)
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return -ENOMEM;
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+ /* prepare oldtnode to be freed */
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+ tnode_free_init(oldtnode);
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+
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/* Assemble all of the pointers in our cluster, in this case that
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* represents all of the pointers out of our allocated nodes that
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* point to existing tnodes and the links between our allocated
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* nodes.
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*/
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for (i = tnode_child_length(oldtnode), m = 1u << tn->pos; i;) {
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- inode = tnode_get_child(oldtnode, --i);
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+ struct tnode *inode = tnode_get_child(oldtnode, --i);
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+ struct tnode *node0, *node1;
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+ unsigned long j, k;
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/* An empty child */
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if (inode == NULL)
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@@ -464,6 +516,9 @@ static int inflate(struct trie *t, struc
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continue;
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}
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+ /* drop the node in the old tnode free list */
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+ tnode_free_append(oldtnode, inode);
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+
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/* An internal node with two children */
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if (inode->bits == 1) {
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put_child(tn, 2 * i + 1, tnode_get_child(inode, 1));
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@@ -488,9 +543,9 @@ static int inflate(struct trie *t, struc
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node1 = tnode_new(inode->key | m, inode->pos, inode->bits - 1);
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if (!node1)
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goto nomem;
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- tnode_free_append(tn, node1);
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+ node0 = tnode_new(inode->key, inode->pos, inode->bits - 1);
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- node0 = tnode_new(inode->key & ~m, inode->pos, inode->bits - 1);
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+ tnode_free_append(tn, node1);
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if (!node0)
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goto nomem;
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tnode_free_append(tn, node0);
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@@ -512,53 +567,9 @@ static int inflate(struct trie *t, struc
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put_child(tn, 2 * i, node0);
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}
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- /* setup the parent pointer into and out of this node */
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- tp = node_parent(oldtnode);
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- NODE_INIT_PARENT(tn, tp);
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- put_child_root(tp, t, tn->key, tn);
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+ /* setup the parent pointers into and out of this node */
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+ replace(t, oldtnode, tn);
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- /* prepare oldtnode to be freed */
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- tnode_free_init(oldtnode);
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-
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- /* update all child nodes parent pointers to route to us */
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- for (i = tnode_child_length(oldtnode); i;) {
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- inode = tnode_get_child(oldtnode, --i);
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-
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- /* A leaf or an internal node with skipped bits */
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- if (!tnode_full(oldtnode, inode)) {
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- node_set_parent(inode, tn);
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- continue;
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- }
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-
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- /* drop the node in the old tnode free list */
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- tnode_free_append(oldtnode, inode);
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-
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- /* fetch new nodes */
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- node1 = tnode_get_child(tn, 2 * i + 1);
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- node0 = tnode_get_child(tn, 2 * i);
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-
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- /* bits == 1 then node0 and node1 represent inode's children */
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- if (inode->bits == 1) {
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- node_set_parent(node1, tn);
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- node_set_parent(node0, tn);
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- continue;
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- }
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-
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- /* update parent pointers in child node's children */
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- for (k = tnode_child_length(inode), j = k / 2; j;) {
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- node_set_parent(tnode_get_child(inode, --k), node1);
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- node_set_parent(tnode_get_child(inode, --j), node0);
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- node_set_parent(tnode_get_child(inode, --k), node1);
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- node_set_parent(tnode_get_child(inode, --j), node0);
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- }
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-
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- /* resize child nodes */
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- resize(t, node1);
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- resize(t, node0);
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- }
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-
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- /* we completed without error, prepare to free old node */
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- tnode_free(oldtnode);
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return 0;
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nomem:
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/* all pointers should be clean so we are done */
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@@ -568,7 +579,7 @@ nomem:
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static int halve(struct trie *t, struct tnode *oldtnode)
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{
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- struct tnode *tn, *tp, *inode, *node0, *node1;
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+ struct tnode *tn;
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unsigned long i;
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pr_debug("In halve\n");
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@@ -577,14 +588,18 @@ static int halve(struct trie *t, struct
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if (!tn)
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return -ENOMEM;
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+ /* prepare oldtnode to be freed */
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+ tnode_free_init(oldtnode);
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+
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/* Assemble all of the pointers in our cluster, in this case that
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* represents all of the pointers out of our allocated nodes that
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* point to existing tnodes and the links between our allocated
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* nodes.
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*/
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for (i = tnode_child_length(oldtnode); i;) {
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- node1 = tnode_get_child(oldtnode, --i);
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- node0 = tnode_get_child(oldtnode, --i);
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+ struct tnode *node1 = tnode_get_child(oldtnode, --i);
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+ struct tnode *node0 = tnode_get_child(oldtnode, --i);
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+ struct tnode *inode;
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/* At least one of the children is empty */
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if (!node1 || !node0) {
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@@ -609,34 +624,8 @@ static int halve(struct trie *t, struct
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put_child(tn, i / 2, inode);
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}
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- /* setup the parent pointer out of and back into this node */
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- tp = node_parent(oldtnode);
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- NODE_INIT_PARENT(tn, tp);
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- put_child_root(tp, t, tn->key, tn);
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-
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- /* prepare oldtnode to be freed */
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- tnode_free_init(oldtnode);
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-
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- /* update all of the child parent pointers */
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- for (i = tnode_child_length(tn); i;) {
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- inode = tnode_get_child(tn, --i);
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-
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- /* only new tnodes will be considered "full" nodes */
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- if (!tnode_full(tn, inode)) {
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- node_set_parent(inode, tn);
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- continue;
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- }
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-
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- /* Two nonempty children */
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- node_set_parent(tnode_get_child(inode, 1), inode);
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- node_set_parent(tnode_get_child(inode, 0), inode);
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-
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- /* resize child node */
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- resize(t, inode);
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- }
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-
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- /* all pointers should be clean so we are done */
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- tnode_free(oldtnode);
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+ /* setup the parent pointers into and out of this node */
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+ replace(t, oldtnode, tn);
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return 0;
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}
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