From c4b2c0c5f647aa1093e8f9097a30c17ce0f94d4d Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Sat, 19 Oct 2013 21:48:53 +0200 Subject: [PATCH] static_key: WARN on usage before jump_label_init was called Usage of the static key primitives to toggle a branch must not be used before jump_label_init() is called from init/main.c. jump_label_init reorganizes and wires up the jump_entries so usage before that could have unforeseen consequences. Following primitives are now checked for correct use: * static_key_slow_inc * static_key_slow_dec * static_key_slow_dec_deferred * jump_label_rate_limit The x86 architecture already checks this by testing if the default_nop was already replaced with an optimal nop or with a branch instruction. It will panic then. Other architectures don't check for this. Because we need to relax this check for the x86 arch to allow code to transition from default_nop to the enabled state and other architectures did not check for this at all this patch introduces checking on the static_key primitives in a non-arch dependent manner. All checked functions are considered slow-path so the additional check does no harm to performance. The warnings are best observed with earlyprintk. Based on a patch from Andi Kleen. Cc: Steven Rostedt Cc: Peter Zijlstra Cc: Andi Kleen Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- include/linux/jump_label.h | 10 ++++++++++ include/linux/jump_label_ratelimit.h | 2 ++ init/main.c | 7 +++++++ kernel/jump_label.c | 5 +++++ 4 files changed, 24 insertions(+) diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index a5079072da66..e96be7245717 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -48,6 +48,13 @@ #include #include +#include + +extern bool static_key_initialized; + +#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ + "%s used before call to jump_label_init", \ + __func__) #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) @@ -128,6 +135,7 @@ struct static_key { static __always_inline void jump_label_init(void) { + static_key_initialized = true; } static __always_inline bool static_key_false(struct static_key *key) @@ -146,11 +154,13 @@ static __always_inline bool static_key_true(struct static_key *key) static inline void static_key_slow_inc(struct static_key *key) { + STATIC_KEY_CHECK_USE(); atomic_inc(&key->enabled); } static inline void static_key_slow_dec(struct static_key *key) { + STATIC_KEY_CHECK_USE(); atomic_dec(&key->enabled); } diff --git a/include/linux/jump_label_ratelimit.h b/include/linux/jump_label_ratelimit.h index 113788389b3d..089f70f83e97 100644 --- a/include/linux/jump_label_ratelimit.h +++ b/include/linux/jump_label_ratelimit.h @@ -23,12 +23,14 @@ struct static_key_deferred { }; static inline void static_key_slow_dec_deferred(struct static_key_deferred *key) { + STATIC_KEY_CHECK_USE(); static_key_slow_dec(&key->key); } static inline void jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl) { + STATIC_KEY_CHECK_USE(); } #endif /* HAVE_JUMP_LABEL */ #endif /* _LINUX_JUMP_LABEL_RATELIMIT_H */ diff --git a/init/main.c b/init/main.c index af310afbef28..27bbec1a5b35 100644 --- a/init/main.c +++ b/init/main.c @@ -135,6 +135,13 @@ static char *static_command_line; static char *execute_command; static char *ramdisk_execute_command; +/* + * Used to generate warnings if static_key manipulation functions are used + * before jump_label_init is called. + */ +bool static_key_initialized __read_mostly = false; +EXPORT_SYMBOL_GPL(static_key_initialized); + /* * If set, this is an indication to the drivers that reset the underlying * device before going ahead with the initialization otherwise driver might diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 297a9247a3b3..9019f15deab2 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -58,6 +58,7 @@ static void jump_label_update(struct static_key *key, int enable); void static_key_slow_inc(struct static_key *key) { + STATIC_KEY_CHECK_USE(); if (atomic_inc_not_zero(&key->enabled)) return; @@ -103,12 +104,14 @@ static void jump_label_update_timeout(struct work_struct *work) void static_key_slow_dec(struct static_key *key) { + STATIC_KEY_CHECK_USE(); __static_key_slow_dec(key, 0, NULL); } EXPORT_SYMBOL_GPL(static_key_slow_dec); void static_key_slow_dec_deferred(struct static_key_deferred *key) { + STATIC_KEY_CHECK_USE(); __static_key_slow_dec(&key->key, key->timeout, &key->work); } EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred); @@ -116,6 +119,7 @@ EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred); void jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl) { + STATIC_KEY_CHECK_USE(); key->timeout = rl; INIT_DELAYED_WORK(&key->work, jump_label_update_timeout); } @@ -212,6 +216,7 @@ void __init jump_label_init(void) key->next = NULL; #endif } + static_key_initialized = true; jump_label_unlock(); } -- 2.30.2