[PATCH RFC V4 06/10] jump_label: add arch_jump_label_transform_static() to optimise non-live code updates

Jeremy Fitzhardinge
2011-10-13T00:09:03Z

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

When updating a newly loaded module, the code is definitely not yet
executing on any processor, so it can be updated with no need for any
heavyweight synchronization.

This patch adds arch_jump_label_static() which is implemented as
arch_jump_label_transform() by default, but architectures can override
it if it avoids, say, a call to stop_machine().

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Jason Baron <jbaron@redhat.com>
---
include/linux/jump_label.h | 2 ++
kernel/jump_label.c | 18 +++++++++++++++---
2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 12e804e..56594e4 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -45,6 +45,8 @@ extern void jump_label_lock(void);
extern void jump_label_unlock(void);
extern void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type);
+extern void arch_jump_label_transform_static(struct jump_entry *entry,
+ enum jump_label_type type);
extern int jump_label_text_reserved(void *start, void *end);
extern void jump_label_inc(struct jump_label_key *key);
extern void jump_label_dec(struct jump_label_key *key);
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 059202d5..ff2028f 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -104,6 +104,18 @@ static int __jump_label_text_reserved(struct jump_entry *iter_start,
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
+ * cheaper.
+ */
+void __weak arch_jump_label_transform_static(struct jump_entry *entry,
+ enum jump_label_type type)
+{
+ arch_jump_label_transform(entry, type);
+}
+
static void __jump_label_update(struct jump_label_key *key,
struct jump_entry *entry,
struct jump_entry *stop, int enable)
@@ -135,8 +147,8 @@ static __init int jump_label_init(void)
struct jump_label_key *iterk;

iterk = (struct jump_label_key *)(unsigned long)iter->key;
- arch_jump_label_transform(iter, jump_label_enabled(iterk) ?
- JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
+ arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
+ JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
if (iterk == key)
continue;

@@ -208,7 +220,7 @@ void jump_label_apply_nops(struct module *mod)
return;

for (iter = iter_start; iter < iter_stop; iter++)
- arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
+ arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
}

static int jump_label_add_module(struct module *mod)
--
1.7.6.4