Re: [RFC][PATCH 5/7] jump_label: Rework update logic

[Peter Zijlstra <peterz@infradead.org>]

Fixes jump_label_add_module()

---
Subject: jump_label: Rework update logic
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri Jul 24 15:06:37 CEST 2015

Instead of spreading the branch_default logic all over the place,
concentrate it into the one jump_label_type() function.

This does mean we need to actually increment/decrement they enabled
count _before_ calling the update path, otherwise jump_label_type()
will not see the right state.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/jump_label.c |   88 ++++++++++++++++++++++------------------------------
 1 file changed, 38 insertions(+), 50 deletions(-)

--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -54,12 +54,7 @@ jump_label_sort_entries(struct jump_entr
 	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
 }
 
-static void jump_label_update(struct static_key *key, int enable);
-
-static inline bool static_key_type(struct static_key *key)
-{
-	return (unsigned long)key->entries & JUMP_TYPE_MASK;
-}
+static void jump_label_update(struct static_key *key);
 
 void static_key_slow_inc(struct static_key *key)
 {
@@ -68,13 +63,8 @@ void static_key_slow_inc(struct static_k
 		return;
 
 	jump_label_lock();
-	if (atomic_read(&key->enabled) == 0) {
-		if (!static_key_type(key))
-			jump_label_update(key, JUMP_LABEL_JMP);
-		else
-			jump_label_update(key, JUMP_LABEL_NOP);
-	}
-	atomic_inc(&key->enabled);
+	if (atomic_inc_and_test(&key->enabled))
+		jump_label_update(key);
 	jump_label_unlock();
 }
 EXPORT_SYMBOL_GPL(static_key_slow_inc);
@@ -92,10 +82,7 @@ static void __static_key_slow_dec(struct
 		atomic_inc(&key->enabled);
 		schedule_delayed_work(work, rate_limit);
 	} else {
-		if (!static_key_type(key))
-			jump_label_update(key, JUMP_LABEL_NOP);
-		else
-			jump_label_update(key, JUMP_LABEL_JMP);
+		jump_label_update(key);
 	}
 	jump_label_unlock();
 }
@@ -154,7 +141,7 @@ static int __jump_label_text_reserved(st
 	return 0;
 }
 
-/* 
+/*
  * Update code which is definitely not currently executing.
  * Architectures which need heavyweight synchronization to modify
  * running code can override this to make the non-live update case
@@ -163,29 +150,17 @@ static int __jump_label_text_reserved(st
 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 					    enum jump_label_type type)
 {
-	arch_jump_label_transform(entry, type);	
+	arch_jump_label_transform(entry, type);
 }
 
-static void __jump_label_update(struct static_key *key,
-				struct jump_entry *entry,
-				struct jump_entry *stop, int enable)
+static inline struct jump_entry *static_key_entries(struct static_key *key)
 {
-	for (; (entry < stop) &&
-	      (entry->key == (jump_label_t)(unsigned long)key);
-	      entry++) {
-		/*
-		 * entry->code set to 0 invalidates module init text sections
-		 * kernel_text_address() verifies we are not in core kernel
-		 * init code, see jump_label_invalidate_module_init().
-		 */
-		if (entry->code && kernel_text_address(entry->code))
-			arch_jump_label_transform(entry, enable);
-	}
+	return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
 }
 
-static inline struct jump_entry *static_key_entries(struct static_key *key)
+static inline bool static_key_type(struct static_key *key)
 {
-	return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
+	return (unsigned long)key->entries & JUMP_TYPE_MASK;
 }
 
 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
@@ -193,14 +168,30 @@ static inline struct static_key *jump_en
 	return (struct static_key *)((unsigned long)entry->key);
 }
 
-static enum jump_label_type jump_label_type(struct static_key *key)
+static enum jump_label_type jump_label_type(struct jump_entry *entry)
 {
+	struct static_key *key = jump_entry_key(entry);
 	bool enabled = static_key_enabled(key);
 	bool type = static_key_type(key);
 
 	return enabled ^ type;
 }
 
+static void __jump_label_update(struct static_key *key,
+				struct jump_entry *entry,
+				struct jump_entry *stop)
+{
+	for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
+		/*
+		 * entry->code set to 0 invalidates module init text sections
+		 * kernel_text_address() verifies we are not in core kernel
+		 * init code, see jump_label_invalidate_module_init().
+		 */
+		if (entry->code && kernel_text_address(entry->code))
+			arch_jump_label_transform(entry, jump_label_type(entry));
+	}
+}
+
 void __init jump_label_init(void)
 {
 	struct jump_entry *iter_start = __start___jump_table;
@@ -214,8 +205,8 @@ void __init jump_label_init(void)
 	for (iter = iter_start; iter < iter_stop; iter++) {
 		struct static_key *iterk;
 
+		arch_jump_label_transform_static(iter, jump_label_type(iter));
 		iterk = jump_entry_key(iter);
-		arch_jump_label_transform_static(iter, jump_label_type(iterk));
 		if (iterk == key)
 			continue;
 
@@ -255,17 +246,15 @@ static int __jump_label_mod_text_reserve
 				start, end);
 }
 
-static void __jump_label_mod_update(struct static_key *key, int enable)
+static void __jump_label_mod_update(struct static_key *key)
 {
-	struct static_key_mod *mod = key->next;
+	struct static_key_mod *mod;
 
-	while (mod) {
+	for (mod = key->next; mod; mod = mod->next) {
 		struct module *m = mod->mod;
 
 		__jump_label_update(key, mod->entries,
-				    m->jump_entries + m->num_jump_entries,
-				    enable);
-		mod = mod->next;
+				    m->jump_entries + m->num_jump_entries);
 	}
 }
 
@@ -287,9 +276,8 @@ void jump_label_apply_nops(struct module
 	if (iter_start == iter_stop)
 		return;
 
-	for (iter = iter_start; iter < iter_stop; iter++) {
+	for (iter = iter_start; iter < iter_stop; iter++)
 		arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
-	}
 }
 
 static int jump_label_add_module(struct module *mod)
@@ -330,8 +318,8 @@ static int jump_label_add_module(struct
 		jlm->next = key->next;
 		key->next = jlm;
 
-		if (jump_label_type(key) == JUMP_LABEL_JMP)
-			__jump_label_update(key, iter, iter_stop, JUMP_LABEL_JMP);
+		if (jump_label_type(iter) == JUMP_LABEL_JMP)
+			__jump_label_update(key, iter, iter_stop);
 	}
 
 	return 0;
@@ -451,14 +439,14 @@ int jump_label_text_reserved(void *start
 	return ret;
 }
 
-static void jump_label_update(struct static_key *key, int enable)
+static void jump_label_update(struct static_key *key)
 {
 	struct jump_entry *stop = __stop___jump_table;
 	struct jump_entry *entry = static_key_entries(key);
 #ifdef CONFIG_MODULES
 	struct module *mod;
 
-	__jump_label_mod_update(key, enable);
+	__jump_label_mod_update(key);
 
 	preempt_disable();
 	mod = __module_address((unsigned long)key);
@@ -468,7 +456,7 @@ static void jump_label_update(struct sta
 #endif
 	/* if there are no users, entry can be NULL */
 	if (entry)
-		__jump_label_update(key, entry, stop, enable);
+		__jump_label_update(key, entry, stop);
 }
 
 #endif