[PATCH 3.16 14/86] locking/static_keys: Rework update logic

Ben Hutchings
2019-05-16T16:04:41Z

From: Peter Zijlstra <peterz@infradead.org>

commit 706249c222f68471b6f8e9e8e9b77665c404b226 upstream.

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 the 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>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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_return(&key->enabled) == 1)
+ 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();
}
@@ -161,7 +148,7 @@ 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
@@ -170,29 +157,17 @@ 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)
@@ -200,14 +175,30 @@ 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;
@@ -221,8 +212,8 @@ 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;

@@ -262,17 +253,15 @@ 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);
}
}

@@ -294,9 +283,8 @@ 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)
@@ -337,8 +325,8 @@ 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;
@@ -458,14 +446,14 @@ 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);
@@ -475,7 +463,7 @@ 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