Re: [PATCH v4 6/9] rbtree: Implement generic latch_tree

From: Peter Zijlstra
Date: Thu Apr 09 2015 - 08:13:58 EST

On Thu, Apr 09, 2015 at 04:55:05PM +0800, Lai Jiangshan wrote:
> This sentence is talking about module.c not latch_tree.h. So I guess
> it is user(module.c)'s problem, not latch_tree.h's problem.
>
> The user(module.c) can wrap the struct latch_tree_nodes and add @priv.

OK, took me a while to figure out exactly what and how. You mean
something like this, right?

(compile tested only)

---
include/linux/module.h | 11 ++++-
include/linux/rbtree_latch.h | 93 ++++++++++++++++++-------------------------
kernel/module.c | 33 +++++++++------
3 files changed, 70 insertions(+), 67 deletions(-)

--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -211,6 +211,13 @@ enum module_state {
MODULE_STATE_UNFORMED, /* Still setting it up. */
};

+struct module;
+
+struct mod_tree_node {
+ struct latch_tree_node node;
+ struct module *mod;
+};
+
struct module {
enum module_state state;

@@ -294,8 +301,8 @@ struct module {
* core.node[0] to be in the same cacheline as the above entries,
* we also assume ltn_init has a higher address than ltn_core.
*/
- struct latch_tree_nodes ltn_core;
- struct latch_tree_nodes ltn_init;
+ struct mod_tree_node mtn_core;
+ struct mod_tree_node mtn_init;

/* Size of RO sections of the module (text+rodata) */
unsigned int init_ro_size, core_ro_size;
--- a/include/linux/rbtree_latch.h
+++ b/include/linux/rbtree_latch.h
@@ -36,17 +36,7 @@
#include <linux/seqlock.h>

struct latch_tree_node {
- /*
- * Because we have an array of two entries in struct latch_tree_nodes
- * it's not possible to use container_of() to get back to the
- * encapsulating structure; therefore we have to put in a back pointer.
- */
- void *priv;
- struct rb_node node;
-};
-
-struct latch_tree_nodes {
- struct latch_tree_node node[2];
+ struct rb_node node[2];
};

struct latch_tree_root {
@@ -74,17 +64,25 @@ struct latch_tree_ops {
int (*comp)(void *key, struct latch_tree_node *b);
};

+static __always_inline struct latch_tree_node *
+__lt_from_rb(struct rb_node *node, int idx)
+{
+ return container_of(node, struct latch_tree_node, node[idx]);
+}
+
static __always_inline void
-__lt_insert(struct latch_tree_node *ltn, struct rb_root *root,
+__lt_insert(struct latch_tree_node *ltn, struct latch_tree_root *ltr, int idx,
bool (*less)(struct latch_tree_node *a, struct latch_tree_node *b))
{
+ struct rb_root *root = &ltr->tree[idx];
struct rb_node **link = &root->rb_node;
+ struct rb_node *node = &ltn->node[idx];
struct rb_node *parent = NULL;
struct latch_tree_node *ltp;

while (*link) {
parent = *link;
- ltp = container_of(parent, struct latch_tree_node, node);
+ ltp = __lt_from_rb(parent, idx);

if (less(ltn, ltp))
link = &parent->rb_left;
@@ -92,32 +90,32 @@ __lt_insert(struct latch_tree_node *ltn,
link = &parent->rb_right;
}

- rb_link_node_rcu(&ltn->node, parent, link);
- rb_insert_color(&ltn->node, root);
+ rb_link_node_rcu(node, parent, link);
+ rb_insert_color(node, root);
}

static __always_inline void
-__lt_erase(struct latch_tree_node *ltn, struct rb_root *root)
+__lt_erase(struct latch_tree_node *ltn, struct latch_tree_root *ltr, int idx)
{
- rb_erase(&ltn->node, root);
+ rb_erase(&ltn->node[idx], &ltr->tree[idx]);
}

static __always_inline struct latch_tree_node *
-__lt_find(void *key, struct rb_root *root,
- int (*comp)(void *key, struct latch_tree_node *ltn))
+__lt_find(void *key, struct latch_tree_root *ltr, int idx,
+ int (*comp)(void *key, struct latch_tree_node *node))
{
- struct rb_node *n = rcu_dereference_raw(root->rb_node);
+ struct rb_node *node = rcu_dereference_raw(ltr->tree[idx].rb_node);
struct latch_tree_node *ltn;
int c;

- while (n) {
- ltn = container_of(n, struct latch_tree_node, node);
+ while (node) {
+ ltn = __lt_from_rb(node, idx);
c = comp(key, ltn);

if (c < 0)
- n = rcu_dereference_raw(n->rb_left);
+ node = rcu_dereference_raw(node->rb_left);
else if (c > 0)
- n = rcu_dereference_raw(n->rb_right);
+ node = rcu_dereference_raw(node->rb_right);
else
return ltn;
}
@@ -126,65 +124,56 @@ __lt_find(void *key, struct rb_root *roo
}

/**
- * latch_tree_insert() - insert @nodes into the trees @root
- * @nodes: nodes to insert
- * @root: trees to insert @nodes into
- * @priv: pointer to node private data
+ * latch_tree_insert() - insert @node into the trees @root
+ * @node: nodes to insert
+ * @root: trees to insert @node into
* @ops: operators defining the node order
*
- * Initializes @nodes private pointer with @priv; which typically is a back
- * pointer to the containing structure, used by @ops to find the search key.
+ * It inserts @node into @root in an ordered fashion such that we can always
+ * observe one complete tree. See the comment for raw_write_seqcount_latch().
*
- * Then it inserts @nodes into @root in an ordered fashion such that we can
- * always observe one complete tree. See the comment for
- * raw_write_seqcount_latch().
- *
- * The inserts use rcu_assign_pointer() to publish the element such that
- * both the @priv pointer values in @nodes as the tree structure is stored
- * before we can observe the new @nodes.
+ * The inserts use rcu_assign_pointer() to publish the element such that the
+ * tree structure is stored before we can observe the new @node.
*
* All modifications (latch_tree_insert, latch_tree_remove) are assumed to be
* serialized.
*/
static __always_inline void
-latch_tree_insert(struct latch_tree_nodes *nodes,
+latch_tree_insert(struct latch_tree_node *node,
struct latch_tree_root *root,
- void *priv,
const struct latch_tree_ops *ops)
{
- nodes->node[0].priv = nodes->node[1].priv = priv;
-
raw_write_seqcount_latch(&root->seq);
- __lt_insert(&nodes->node[0], &root->tree[0], ops->less);
+ __lt_insert(node, root, 0, ops->less);
raw_write_seqcount_latch(&root->seq);
- __lt_insert(&nodes->node[1], &root->tree[1], ops->less);
+ __lt_insert(node, root, 1, ops->less);
}

/**
- * latch_tree_erase() - removes @nodes from the trees @root
- * @nodes: nodes to remote
- * @root: trees to remove @nodes from
+ * latch_tree_erase() - removes @node from the trees @root
+ * @node: nodes to remote
+ * @root: trees to remove @node from
* @ops: operators defining the node order
*
- * Removes @nodes from the trees @root in an ordered fashion such that we can
+ * Removes @node from the trees @root in an ordered fashion such that we can
* always observe one complete tree. See the comment for
* raw_write_seqcount_latch().
*
- * It is assumed that @nodes will observe one RCU quiescent state before being
+ * It is assumed that @node will observe one RCU quiescent state before being
* reused of freed.
*
* All modifications (latch_tree_insert, latch_tree_remove) are assumed to be
* serialized.
*/
static __always_inline void
-latch_tree_erase(struct latch_tree_nodes *nodes,
+latch_tree_erase(struct latch_tree_node *node,
struct latch_tree_root *root,
const struct latch_tree_ops *ops)
{
raw_write_seqcount_latch(&root->seq);
- __lt_erase(&nodes->node[0], &root->tree[0]);
+ __lt_erase(node, root, 0);
raw_write_seqcount_latch(&root->seq);
- __lt_erase(&nodes->node[1], &root->tree[1]);
+ __lt_erase(node, root, 1);
}

/**
@@ -214,7 +203,7 @@ latch_tree_find(void *key, struct latch_

do {
seq = raw_read_seqcount(&root->seq);
- node = __lt_find(key, &root->tree[seq & 1], ops->comp);
+ node = __lt_find(key, root, seq & 1, ops->comp);
} while (read_seqcount_retry(&root->seq, seq));

return node;
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -119,22 +119,24 @@ static LIST_HEAD(modules);

static __always_inline unsigned long __mod_tree_val(struct latch_tree_node *n)
{
- struct module *mod = n->priv;
+ struct mod_tree_node *mtn = container_of(n, struct mod_tree_node, node);
+ struct module *mod = mtn->mod;

- if (n >= mod->ltn_init.node)
+ if (unlikely(mtn == &mod->mtn_init))
return (unsigned long)mod->module_init;
- else
- return (unsigned long)mod->module_core;
+
+ return (unsigned long)mod->module_core;
}

static __always_inline unsigned long __mod_tree_size(struct latch_tree_node *n)
{
- struct module *mod = n->priv;
+ struct mod_tree_node *mtn = container_of(n, struct mod_tree_node, node);
+ struct module *mod = mtn->mod;

- if (n >= mod->ltn_init.node)
+ if (unlikely(mtn == &mod->mtn_init))
return (unsigned long)mod->init_size;
- else
- return (unsigned long)mod->core_size;
+
+ return (unsigned long)mod->core_size;
}

static __always_inline bool
@@ -174,20 +176,23 @@ static struct latch_tree_root mod_tree _
*/
static void mod_tree_insert(struct module *mod)
{
- latch_tree_insert(&mod->ltn_core, &mod_tree, mod, &mod_tree_ops);
+ mod->mtn_core.mod = mod;
+ mod->mtn_init.mod = mod;
+
+ latch_tree_insert(&mod->mtn_core.node, &mod_tree, &mod_tree_ops);
if (mod->init_size)
- latch_tree_insert(&mod->ltn_init, &mod_tree, mod, &mod_tree_ops);
+ latch_tree_insert(&mod->mtn_init.node, &mod_tree, &mod_tree_ops);
}

static void mod_tree_remove_init(struct module *mod)
{
if (mod->init_size)
- latch_tree_erase(&mod->ltn_init, &mod_tree, &mod_tree_ops);
+ latch_tree_erase(&mod->mtn_init.node, &mod_tree, &mod_tree_ops);
}

static void mod_tree_remove(struct module *mod)
{
- latch_tree_erase(&mod->ltn_core, &mod_tree, &mod_tree_ops);
+ latch_tree_erase(&mod->mtn_core.node, &mod_tree, &mod_tree_ops);
mod_tree_remove_init(mod);
}

@@ -196,8 +201,10 @@ static struct module *mod_find(unsigned
struct latch_tree_node *ltn;

ltn = latch_tree_find((void *)addr, &mod_tree, &mod_tree_ops);
+ if (!ltn)
+ return NULL;

- return ltn ? ltn->priv : NULL;
+ return container_of(ltn, struct mod_tree_node, node)->mod;
}

#else /* !(PERF_EVENTS || TRACING) */
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/