latched RB-trees and __module_address()

@@ -415,14 +415,22 @@ struct symsearch {
 	bool unused;
 };
 
-/* Search for an exported symbol by name. */
+/*
+ * Search for an exported symbol by name.
+ *
+ * Must be called with module_mutex held or preemption disabled.
+ */
 const struct kernel_symbol *find_symbol(const char *name,
 					struct module **owner,
 					const unsigned long **crc,
 					bool gplok,
 					bool warn);
 
-/* Walk the exported symbol table */
+/*
+ * Walk the exported symbol table
+ *
+ * Must be called with module_mutex held or preemption disabled.
+ */
 bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
 				    struct module *owner,
 				    void *data), void *data);

91 lines not on this page · raw message

@@ -66,7 +66,7 @@ static const struct bug_entry *module_fi
 	struct module *mod;
 	const struct bug_entry *bug = NULL;
 
-	rcu_read_lock();
+	rcu_read_lock_sched();
 	list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
 		unsigned i;
 

@@ -77,7 +77,7 @@ static const struct bug_entry *module_fi
 	}
 	bug = NULL;
 out:
-	rcu_read_unlock();
+	rcu_read_unlock_sched();
 
 	return bug;
 }

@@ -88,6 +88,8 @@ void module_bug_finalize(const Elf_Ehdr
 	char *secstrings;
 	unsigned int i;
 
+	lockdep_assert_held(&module_mutex);
+
 	mod->bug_table = NULL;
 	mod->num_bugs = 0;
 

@@ -113,6 +115,7 @@ void module_bug_finalize(const Elf_Ehdr
 
 void module_bug_cleanup(struct module *mod)
 {
+	lockdep_assert_held(&module_mutex);
 	list_del_rcu(&mod->bug_list);
 }
 

@@ -1191,11 +1191,17 @@ static inline int check_modstruct_versio
 {
 	const unsigned long *crc;
 
-	/* Since this should be found in kernel (which can't be removed),
-	 * no locking is necessary. */
+	/*
+	 * Since this should be found in kernel (which can't be removed), no
+	 * locking is necessary -- use preempt_disable() to placate lockdep.
+	 */
+	preempt_disable();
 	if (!find_symbol(VMLINUX_SYMBOL_STR(module_layout), NULL,
-			 &crc, true, false))
+			 &crc, true, false)) {
+		preempt_enable();
 		BUG();
+	}
+	preempt_enable();
 	return check_version(sechdrs, versindex,
 			     VMLINUX_SYMBOL_STR(module_layout), mod, crc,
 			     NULL);

@@ -302,7 +302,7 @@ static int jump_label_add_module(struct
 			continue;
 
 		key = iterk;
-		if (__module_address(iter->key) == mod) {
+		if (within_module(iter->key, mod)) {
 			/*
 			 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 			 */

@@ -339,7 +339,7 @@ static void jump_label_del_module(struct
 
 		key = (struct static_key *)(unsigned long)iter->key;
 
-		if (__module_address(iter->key) == mod)
+		if (within_module(iter->key, mod))
 			continue;
 
 		prev = &key->next;

@@ -443,14 +443,16 @@ static void jump_label_update(struct sta
 {
 	struct jump_entry *stop = __stop___jump_table;
 	struct jump_entry *entry = jump_label_get_entries(key);
-
 #ifdef CONFIG_MODULES
-	struct module *mod = __module_address((unsigned long)key);
+	struct module *mod;
 
 	__jump_label_mod_update(key, enable);
 
+	preempt_disable();
+	mod = __module_address((unsigned long)key);
 	if (mod)
 		stop = mod->jump_entries + mod->num_jump_entries;
+	preempt_enable();
 #endif
 	/* if there are no users, entry can be NULL */
 	if (entry)

@@ -31,6 +31,7 @@
 
 #include <linux/kernel.h>
 #include <linux/stddef.h>
+#include <linux/rcupdate.h>
 
 struct rb_node {
 	unsigned long  __rb_parent_color;

@@ -85,6 +86,15 @@ static inline void rb_link_node(struct r
 	*rb_link = node;
 }
 
+static inline void rb_link_node_rcu(struct rb_node * node, struct rb_node * parent,
+				    struct rb_node ** rb_link)
+{
+	node->__rb_parent_color = (unsigned long)parent;
+	node->rb_left = node->rb_right = NULL;
+
+	rcu_assign_pointer(*rb_link, node);
+}
+
 #define rb_entry_safe(ptr, type, member) \
 	({ typeof(ptr) ____ptr = (ptr); \
 	   ____ptr ? rb_entry(____ptr, type, member) : NULL; \

@@ -123,11 +123,11 @@ __rb_change_child(struct rb_node *old, s
 {
 	if (parent) {
 		if (parent->rb_left == old)
-			parent->rb_left = new;
+			WRITE_ONCE(parent->rb_left, new);
 		else
-			parent->rb_right = new;
+			WRITE_ONCE(parent->rb_right, new);
 	} else
-		root->rb_node = new;
+		WRITE_ONCE(root->rb_node, new);
 }
 
 extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,

@@ -137,7 +137,8 @@ static __always_inline struct rb_node *
 __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 		     const struct rb_augment_callbacks *augment)
 {
-	struct rb_node *child = node->rb_right, *tmp = node->rb_left;
+	struct rb_node *child = node->rb_right;
+	struct rb_node *tmp = node->rb_left;
 	struct rb_node *parent, *rebalance;
 	unsigned long pc;
 

@@ -167,6 +168,7 @@ __rb_erase_augmented(struct rb_node *nod
 		tmp = parent;
 	} else {
 		struct rb_node *successor = child, *child2;
+
 		tmp = child->rb_left;
 		if (!tmp) {
 			/*

@@ -180,6 +182,7 @@ __rb_erase_augmented(struct rb_node *nod
 			 */
 			parent = successor;
 			child2 = successor->rb_right;
+
 			augment->copy(node, successor);
 		} else {
 			/*

@@ -201,19 +204,23 @@ __rb_erase_augmented(struct rb_node *nod
 				successor = tmp;
 				tmp = tmp->rb_left;
 			} while (tmp);
-			parent->rb_left = child2 = successor->rb_right;
-			successor->rb_right = child;
+			child2 = successor->rb_right;
+			WRITE_ONCE(parent->rb_left, child2);
+			WRITE_ONCE(successor->rb_right, child);
 			rb_set_parent(child, successor);
+
 			augment->copy(node, successor);
 			augment->propagate(parent, successor);
 		}
 
-		successor->rb_left = tmp = node->rb_left;
+		tmp = node->rb_left;
+		WRITE_ONCE(successor->rb_left, tmp);
 		rb_set_parent(tmp, successor);
 
 		pc = node->__rb_parent_color;
 		tmp = __rb_parent(pc);
 		__rb_change_child(node, successor, tmp, root);
+
 		if (child2) {
 			successor->__rb_parent_color = pc;
 			rb_set_parent_color(child2, parent, RB_BLACK);

142 lines not on this page · raw message

@@ -233,9 +233,83 @@ static inline void raw_write_seqcount_en
 	s->sequence++;
 }
 
-/*
+/**
  * raw_write_seqcount_latch - redirect readers to even/odd copy
  * @s: pointer to seqcount_t
+ *
+ * The latch technique is a multiversion concurrency control method that allows
+ * queries during non atomic modifications. If you can guarantee queries never
+ * interrupt the modification -- e.g. the concurrency is strictly between CPUs
+ * -- you most likely do not need this.
+ *
+ * Where the traditional RCU/lockless data structures rely on atomic
+ * modifications to ensure queries observe either the old or the new state the
+ * latch allows the same for non atomic updates. The trade-off is doubling the
+ * cost of storage; we have to maintain two copies of the entire data
+ * structure.
+ *
+ * Very simply put: we first modify one copy and then the other. This ensures
+ * there is always one copy in a stable state, ready to give us an answer.
+ *
+ * The basic form is a data structure like:
+ *
+ * struct latch_struct {
+ *	seqcount_t		seq;
+ *	struct data_struct	data[2];
+ * };
+ *
+ * Where a modification, which is assumed to be externally serialized, does the
+ * following:
+ *
+ * void latch_modify(struct latch_struct *latch, ...)
+ * {
+ *	smp_wmb();	<- Ensure that the last data[1] update is visible
+ *	latch->seq++;
+ *	smp_wmb();	<- Ensure that the seqcount update is visible
+ *
+ *	modify(latch->data[0], ...);
+ *
+ *	smp_wmb();	<- Ensure that the data[0] update is visible
+ *	latch->seq++;
+ *	smp_wmb();	<- Ensure that the seqcount update is visible
+ *
+ *	modify(latch->data[1], ...);
+ * }
+ *
+ * The query will have a form like:
+ *
+ * struct entry *latch_query(struct latch_struct *latch, ...)
+ * {
+ *	struct entry *entry;
+ *	unsigned seq, idx;
+ *
+ *	do {
+ *		seq = latch->seq;
+ *		smp_rmb();
+ *
+ *		idx = seq & 0x01;
+ *		entry = data_query(latch->data[idx], ...);
+ *
+ *		smp_rmb();
+ *	} while (seq != latch->seq);
+ *
+ *	return entry;
+ * }
+ *
+ * So during the modification, queries are first redirected to data[1]. Then we
+ * modify data[0]. When that is complete, we redirect queries back to data[0]
+ * and we can modify data[1].
+ *
+ * NOTE: The non-requirement for atomic modifications does _NOT_ include
+ *       the publishing of new entries in the case where data is a dynamic
+ *       data structure.
+ *
+ *       An iteration might start in data[0] and get suspended long enough
+ *       to miss an entire modification sequence, once it resumes it might
+ *       observe the new entry.
+ *
+ * NOTE: When data is a dynamic data structure; one should use regular RCU
+ *       patterns to manage the lifetimes of the objects within.
  */
 static inline void raw_write_seqcount_latch(seqcount_t *s)
 {

@@ -339,32 +339,7 @@ static inline s64 timekeeping_get_ns_raw
  * We want to use this from any context including NMI and tracing /
  * instrumenting the timekeeping code itself.
  *
- * So we handle this differently than the other timekeeping accessor
- * functions which retry when the sequence count has changed. The
- * update side does:
- *
- * smp_wmb();	<- Ensure that the last base[1] update is visible
- * tkf->seq++;
- * smp_wmb();	<- Ensure that the seqcount update is visible
- * update(tkf->base[0], tkr);
- * smp_wmb();	<- Ensure that the base[0] update is visible
- * tkf->seq++;
- * smp_wmb();	<- Ensure that the seqcount update is visible
- * update(tkf->base[1], tkr);
- *
- * The reader side does:
- *
- * do {
- *	seq = tkf->seq;
- *	smp_rmb();
- *	idx = seq & 0x01;
- *	now = now(tkf->base[idx]);
- *	smp_rmb();
- * } while (seq != tkf->seq)
- *
- * As long as we update base[0] readers are forced off to
- * base[1]. Once base[0] is updated readers are redirected to base[0]
- * and the base[1] update takes place.
+ * Employ the latch technique; see @raw_write_seqcount_latch.
  *
  * So if a NMI hits the update of base[0] then it will use base[1]
  * which is still consistent. In the worst case this can result is a

@@ -0,0 +1,223 @@
+/*
+ * Latched RB-trees
+ *
+ * Copyright (C) 2015 Intel Corp., Peter Zijlstra <[email protected]>
+ *
+ * Since RB-trees have non atomic modifications they're not immediately suited
+ * for RCU/lockless queries. Even though we made RB tree lookups non-fatal for
+ * lockless lookups; we cannot guarantee they return a correct result.
+ *
+ * The simplest solution is a seqlock + rb-tree, this will allow lockless
+ * lookups; but has the constraint (inherent to the seqlock) that read sides
+ * cannot nest in write sides.
+ *
+ * If we need to allow unconditional lookups (say as required for NMI context
+ * usage) we need a more complex setup; this data structure provides this by
+ * employing the latch technique -- see @raw_write_seqcount_latch -- to
+ * implement a latched RB-tree which does allow for unconditional lookups by
+ * virtue of always having (at least) one stable copy of the tree.
+ *
+ * However, while we have the guarantee that there is at all times one stable
+ * copy, this does not guarantee an iteration will not observe modifications.
+ * What might have been a stable copy at the start of the iteration, need not
+ * remain so for the duration of the iteration.
+ *
+ * Therefore, this does require a lockless RB-tree iteration to be non-fatal;
+ * see the comment in lib/rbtree.c. Note however that we only require the first
+ * condition -- not seeing partial stores -- because the latch thing isolates
+ * us from loops. If we were to interrupt a modification the lookup would be
+ * pointed at the stable tree and complete while the modification was halted.
+ */
+
+#ifndef RB_TREE_LATCH_H
+#define RB_TREE_LATCH_H
+
+#include <linux/rbtree.h>
+#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 latch_tree_root {
+	seqcount_t	seq;
+	struct rb_root	tree[2];
+};
+
+/**
+ * latch_tree_ops - operators to define the tree order
+ * @less: used for insertion; provides the (partial) order between two elements.
+ * @comp: used for lookups; provides the order between the search key and an element.
+ *
+ * The operators are related like:
+ *
+ *	comp(a->key,b) < 0  := less(a,b)
+ *	comp(a->key,b) > 0  := less(b,a)
+ *	comp(a->key,b) == 0 := !less(a,b) && !less(b,a)
+ *
+ * If these operators define a partial order on the elements we make no
+ * guarantee on which of the elements matching the key is found. See
+ * latch_tree_find().
+ */
+struct latch_tree_ops {
+	bool (*less)(struct latch_tree_node *a, struct latch_tree_node *b);
+	int  (*comp)(void *key,                 struct latch_tree_node *b);
+};
+
+static __always_inline void
+__lt_insert(struct latch_tree_node *ltn, struct rb_root *root,
+	    bool (*less)(struct latch_tree_node *a, struct latch_tree_node *b))
+{
+	struct rb_node **link = &root->rb_node;
+	struct rb_node *parent = NULL;
+	struct latch_tree_node *ltp;
+
+	while (*link) {
+		parent = *link;
+		ltp = container_of(parent, struct latch_tree_node, node);
+
+		if (less(ltn, ltp))
+			link = &parent->rb_left;
+		else
+			link = &parent->rb_right;
+	}
+
+	rb_link_node_rcu(&ltn->node, parent, link);
+	rb_insert_color(&ltn->node, root);
+}
+
+static __always_inline void
+__lt_erase(struct latch_tree_node *ltn, struct rb_root *root)
+{
+	rb_erase(&ltn->node, root);
+}
+
+static __always_inline struct latch_tree_node *
+__lt_find(void *key, struct rb_root *root,
+	  int (*comp)(void *key, struct latch_tree_node *ltn))
+{
+	struct rb_node *n = rcu_dereference_raw(root->rb_node);
+	struct latch_tree_node *ltn;
+	int c;
+
+	while (n) {
+		ltn = container_of(n, struct latch_tree_node, node);
+		c = comp(key, ltn);
+
+		if (c < 0)
+			n = rcu_dereference_raw(n->rb_left);
+		else if (c > 0)
+			n = rcu_dereference_raw(n->rb_right);
+		else
+			return ltn;
+	}
+
+	return NULL;
+}
+
+/**
+ * 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
+ * @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.
+ *
+ * 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.
+ *
+ * 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,
+		  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);
+	raw_write_seqcount_latch(&root->seq);
+	__lt_insert(&nodes->node[1], &root->tree[1], ops->less);
+}
+
+/**
+ * latch_tree_erase() - removes @nodes from the trees @root
+ * @nodes: nodes to remote
+ * @root: trees to remove @nodes from
+ * @ops: operators defining the node order
+ *
+ * Removes @nodes 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
+ * 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,
+		 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]);
+	raw_write_seqcount_latch(&root->seq);
+	__lt_erase(&nodes->node[1], &root->tree[1]);
+}
+
+/**
+ * latch_tree_find() - find the node matching @key in the trees @root
+ * @key: search key
+ * @root: trees to search for @key
+ * @ops: operators defining the node order
+ *
+ * Does a lockless lookup in the trees @root for the node matching @key.
+ *
+ * It is assumed that this is called while holding the appropriate RCU read
+ * side lock.
+ *
+ * If the operators define a partial order on the elements (there are multiple
+ * elements which have the same key value) it is undefined which of these
+ * elements will be found. Nor is it possible to iterate the tree to find
+ * further elements with the same key value.
+ *
+ * Returns: a pointer to the node matching @key or NULL.
+ */
+static __always_inline struct latch_tree_node *
+latch_tree_find(void *key, struct latch_tree_root *root,
+		const struct latch_tree_ops *ops)
+{
+	struct latch_tree_node *node;
+	unsigned int seq;
+
+	do {
+		seq = raw_read_seqcount(&root->seq);
+		node = __lt_find(key, &root->tree[seq & 1], ops->comp);
+	} while (read_seqcount_retry(&root->seq, seq));
+
+	return node;
+}
+
+#endif /* RB_TREE_LATCH_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;

179 lines not on this page · raw message

@@ -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) */

@@ -17,6 +17,7 @@
 #include <linux/moduleparam.h>
 #include <linux/jump_label.h>
 #include <linux/export.h>
+#include <linux/rbtree_latch.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>

@@ -269,8 +270,15 @@ struct module {
 	/* Startup function. */
 	int (*init)(void);
 
-	/* If this is non-NULL, vfree after init() returns */
-	void *module_init;
+	/*
+	 * If this is non-NULL, vfree after init() returns.
+	 *
+	 * Cacheline align here, such that:
+	 *   module_init, module_core, init_size, core_size,
+	 *   init_text_size, core_text_size and ltn_core.node[0]
+	 * are on the same cacheline.
+	 */
+	void *module_init	____cacheline_aligned;
 
 	/* Here is the actual code + data, vfree'd on unload. */
 	void *module_core;

@@ -281,6 +289,14 @@ struct module {
 	/* The size of the executable code in each section.  */
 	unsigned int init_text_size, core_text_size;
 
+	/*
+	 * We rely on the order of these two entries; not only do we want
+	 * 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;
+
 	/* Size of RO sections of the module (text+rodata) */
 	unsigned int init_ro_size, core_ro_size;
 

@@ -361,7 +377,7 @@ struct module {
 	ctor_fn_t *ctors;
 	unsigned int num_ctors;
 #endif
-};
+} ____cacheline_aligned;
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}
 #endif

145 lines not on this page · raw message

@@ -102,6 +102,8 @@ DEFINE_MUTEX(module_mutex);
 EXPORT_SYMBOL_GPL(module_mutex);
 static LIST_HEAD(modules);
 
+#if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_TRACING)
+
 /*
  * Use a latched RB-tree for __module_address(); this allows us to use
  * RCU-sched lookups of the address from any context.

@@ -109,6 +111,10 @@ static LIST_HEAD(modules);
  * Because modules have two address ranges: init and core, we need two
  * latch_tree_nodes entries. We use the order they appear in struct module to
  * determine if we need to use the init or core values for the comparisons.
+ *
+ * This is conditional on PERF_EVENTS || TRACING because those can really hit
+ * __module_address() hard by doing a lot of stack unwinding; potentially from
+ * NMI context.
  */
 
 static __always_inline unsigned long __mod_tree_val(struct latch_tree_node *n)

@@ -185,7 +191,7 @@ static void mod_tree_remove(struct modul
 	mod_tree_remove_init(mod);
 }
 
-static struct module *mod_tree_find(unsigned long addr)
+static struct module *mod_find(unsigned long addr)
 {
 	struct latch_tree_node *ltn;
 

@@ -194,6 +200,26 @@ static struct module *mod_tree_find(unsi
 	return ltn ? ltn->priv : NULL;
 }
 
+#else /* !(PERF_EVENTS || TRACING) */
+
+static void mod_tree_insert(struct module *mod) { }
+static void mod_tree_remove_init(struct module *mod) { }
+static void mod_tree_remove(struct module *mod) { }
+
+static struct module *mod_find(unsigned long addr)
+{
+	struct module *mod;
+
+	list_for_each_entry_rcu(mod, &modules, list) {
+		if (within_module(addr, mod))
+			return mod;
+	}
+
+	return NULL;
+}
+
+#endif /* !(PERF_EVENTS || TRACING) */
+
 #ifdef CONFIG_KGDB_KDB
 struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
 #endif /* CONFIG_KGDB_KDB */

@@ -3939,7 +3965,7 @@ struct module *__module_address(unsigned
 
 	module_assert_mutex_or_preempt();
 
-	mod = mod_tree_find(addr);
+	mod = mod_find(addr);
 	if (mod) {
 		BUG_ON(!within_module(addr, mod));
 		if (mod->state == MODULE_STATE_UNFORMED)

@@ -3515,19 +3515,15 @@ const char *module_address_lookup(unsign
 			    char **modname,
 			    char *namebuf)
 {
-	struct module *mod;
 	const char *ret = NULL;
+	struct module *mod;
 
 	preempt_disable();
-	list_for_each_entry_rcu(mod, &modules, list) {
-		if (mod->state == MODULE_STATE_UNFORMED)
-			continue;
-		if (within_module(addr, mod)) {
-			if (modname)
-				*modname = mod->name;
-			ret = get_ksymbol(mod, addr, size, offset);
-			break;
-		}
+	mod = __module_address(addr);
+	if (mod) {
+		if (modname)
+			*modname = mod->name;
+		ret = get_ksymbol(mod, addr, size, offset);
 	}
 	/* Make a copy in here where it's safe */
 	if (ret) {

@@ -3535,6 +3531,7 @@ const char *module_address_lookup(unsign
 		ret = namebuf;
 	}
 	preempt_enable();
+
 	return ret;
 }