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Subject[PATCH] jump_label: jump_label for boot options.
I tried to use jump_label for handling memcg's boot options which sets
global variable true/false and never changes after boot. And found jump_table
is larger than expected. This patch is a trial to allow to place jump_table
in .init section. How do you think ?

This patch is based on linux-next.

==
From ed8996892c21d4fec642e4fc80bd3ebdd8a48836 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Date: Thu, 1 Dec 2011 11:08:23 +0900
Subject: [PATCH] jump_label for boot options.

Some boot options exists for enable/disable a functionality which cannot be modified
after boot. Using jump_label for such behavior seems atractive but if caller
of statch_branch() is too much, jump_table can be unexpectedly big.

This patch adds static_branch_init_once(), which places its jump_table
in init section and never be updated after boot.

For MODULES, using usual static_branch().

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
arch/mips/include/asm/jump_label.h | 14 ++++++++++
arch/powerpc/include/asm/jump_label.h | 15 +++++++++++
arch/x86/include/asm/jump_label.h | 15 +++++++++++
include/asm-generic/vmlinux.lds.h | 6 ++++
include/linux/jump_label.h | 39 +++++++++++++++++++++++++++++
kernel/jump_label.c | 43 ++++++++++++++++++++++++++------
6 files changed, 124 insertions(+), 8 deletions(-)
diff --git a/arch/mips/include/asm/jump_label.h b/arch/mips/include/asm/jump_label.h
index 1881b31..dd0b8f0 100644
--- a/arch/mips/include/asm/jump_label.h
+++ b/arch/mips/include/asm/jump_label.h
@@ -33,6 +33,20 @@ l_yes:
return true;
}

+static __always_inline bool
+arch_static_branch_init_once(struct jump_lable_key *key)
+{
+ asm goto("1:\tnop\n\t"
+ "nop\n\t"
+ ".pushsection __jump_table.init, \"aw\"\n\t"
+ WORD_INSN " 1b, %l[l_yes], %0\n\t"
+ ".popsection\n\t"
+ : : "i" (key) : : l_yes);
+ return false;
+l_yes:
+ return true;
+}
+
#endif /* __KERNEL__ */

#ifdef CONFIG_64BIT
diff --git a/arch/powerpc/include/asm/jump_label.h b/arch/powerpc/include/asm/jump_label.h
index 938986e..8557f8a 100644
--- a/arch/powerpc/include/asm/jump_label.h
+++ b/arch/powerpc/include/asm/jump_label.h
@@ -30,6 +30,21 @@ l_yes:
return true;
}

+static __always_inline bool
+arch_static_branch_init_once(struct jump_label_key *key)
+{
+ asm goto("1:\n\t"
+ "nop\n\t"
+ ".pushsection __jump_table.init, \"aw\"\n\t"
+ JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
+ ".popsection \n\t"
+ : : "i" (key) : : l_yes);
+ return false;
+l_yes:
+ return true;
+}
+
+
#ifdef CONFIG_PPC64
typedef u64 jump_label_t;
#else
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index a32b18c..a85ad63 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -25,6 +25,21 @@ l_yes:
return true;
}

+static __always_inline
+bool arch_static_branch_init_once(struct jump_label_key *key)
+{
+ asm goto("1:"
+ JUMP_LABEL_INITIAL_NOP
+ ".pushsection __jump_table.init, \"aw\" \n\t"
+ _ASM_ALIGN "\n\t"
+ _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
+ ".popsection \n\t"
+ : : "i" (key) : : l_yes);
+ return false;
+l_yes:
+ return true;
+}
+
#endif /* __KERNEL__ */

#ifdef CONFIG_X86_64
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b5e2e4c..1635f38 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -651,6 +651,11 @@
*(.security_initcall.init) \
VMLINUX_SYMBOL(__security_initcall_end) = .;

+#define JUMP_LABEL_FOR_INIT \
+ VMLINUX_SYMBOL(__start___jump_table_at_init) = .; \
+ *(__jump_table.init) \
+ VMLINUX_SYMBOL(__stop___jump_table_at_init) = .;
+
#ifdef CONFIG_BLK_DEV_INITRD
#define INIT_RAM_FS \
. = ALIGN(4); \
@@ -799,6 +804,7 @@
INIT_CALLS \
CON_INITCALL \
SECURITY_INITCALL \
+ JUMP_LABEL_FOR_INIT \
INIT_RAM_FS \
}

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 388b0d4..b0f37f3 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -38,8 +38,31 @@ static __always_inline bool static_branch(struct jump_label_key *key)
return arch_static_branch(key);
}

+/*
+ * Use this when you call static_branch() in __init function or
+ * jump_label is only modified by initcalls. jump_label information
+ * will be discarded after boot. But please be careful. jump_label_key
+ * definition itself should *not* be in __init section because a MODULE
+ * may call static_branch_init_once().
+ *
+ * Useful for changing behavior by boot option.
+ */
+#ifndef MODULE
+static __always_inline bool static_branch_init_once(struct jump_label_key *key)
+{
+ return arch_static_branch_init_once(key);
+}
+#else
+static __always_inline bool static_branch_init_once(struct jump_label_key *key)
+{
+ return static_branch(key);
+}
+#endif
+
extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
+extern struct jump_entry __start___jump_table_at_init[];
+extern struct jump_entry __stop___jump_table_at_init[];

extern void jump_label_init(void);
extern void jump_label_lock(void);
@@ -54,6 +77,12 @@ extern void jump_label_dec(struct jump_label_key *key);
extern bool jump_label_enabled(struct jump_label_key *key);
extern void jump_label_apply_nops(struct module *mod);

+/*
+ * For jump_label in init section.
+ * This will call jump_label_inc() for usual section, too.
+ */
+extern void jump_label_inc_once(struct jump_label_key *key);
+
#else /* !HAVE_JUMP_LABEL */

#include <linux/atomic.h>
@@ -75,6 +104,11 @@ static __always_inline bool static_branch(struct jump_label_key *key)
return false;
}

+static __always_inline bool static_branch_init_once(struct jump_label_key *key)
+{
+ return static_branch(key);
+}
+
static inline void jump_label_inc(struct jump_label_key *key)
{
atomic_inc(&key->enabled);
@@ -102,6 +136,11 @@ static inline int jump_label_apply_nops(struct module *mod)
{
return 0;
}
+
+static inline void jump_label_inc_once(struct jump_label_key *key)
+{
+ jump_label_inc(key);
+}
#endif /* HAVE_JUMP_LABEL */

#endif /* _LINUX_JUMP_LABEL_H */
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 66ff710..f0e8231 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -134,15 +134,11 @@ static void __jump_label_update(struct jump_label_key *key,
}
}

-void __init jump_label_init(void)
+void __init jump_label_transform_all(struct jump_entry *iter_start,
+ struct jump_entry *iter_stop)
{
- struct jump_entry *iter_start = __start___jump_table;
- struct jump_entry *iter_stop = __stop___jump_table;
- struct jump_label_key *key = NULL;
struct jump_entry *iter;
-
- jump_label_lock();
- jump_label_sort_entries(iter_start, iter_stop);
+ struct jump_label_key *key = NULL;

for (iter = iter_start; iter < iter_stop; iter++) {
struct jump_label_key *iterk;
@@ -159,6 +155,24 @@ void __init jump_label_init(void)
key->next = NULL;
#endif
}
+
+}
+
+
+void __init jump_label_init(void)
+{
+ struct jump_entry *iter_start = __start___jump_table;
+ struct jump_entry *iter_stop = __stop___jump_table;
+
+
+ jump_label_lock();
+ jump_label_sort_entries(iter_start, iter_stop);
+ jump_label_transform_all(iter_start, iter_stop);
+ /* update jump_table in .init section */
+ iter_start = __start___jump_table_at_init;
+ iter_stop = __stop___jump_table_at_init;
+ jump_label_sort_entries(iter_start, iter_stop);
+ jump_label_transform_all(iter_start, iter_stop);
jump_label_unlock();
}

@@ -381,7 +395,8 @@ int jump_label_text_reserved(void *start, void *end)

static void jump_label_update(struct jump_label_key *key, int enable)
{
- struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
+ struct jump_entry *entry = key->entries;
+ struct jump_entry *stop = __stop___jump_table;

#ifdef CONFIG_MODULES
struct module *mod = __module_address((jump_label_t)key);
@@ -396,4 +411,16 @@ static void jump_label_update(struct jump_label_key *key, int enable)
__jump_label_update(key, entry, stop, enable);
}

+/* for boot options */
+void __init jump_label_init_once(struct jump_label_key *key)
+{
+ struct jump_entry *entry = key->entries;
+ struct jump_entry *stop = __stop___jump_table_at_init;
+
+ if (entry)
+ __jump_label_update(key, entry, stop, JUMP_LABEL_ENABLE);
+
+ jump_label_inc(key);
+}
+
#endif
--
1.7.4.1



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