--- zzzz-none-000/linux-3.10.107/include/linux/jump_label.h 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/include/linux/jump_label.h 2021-02-04 17:41:59.000000000 +0000 @@ -5,52 +5,86 @@ * Jump label support * * Copyright (C) 2009-2012 Jason Baron - * Copyright (C) 2011-2012 Peter Zijlstra + * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra + * + * DEPRECATED API: + * + * The use of 'struct static_key' directly, is now DEPRECATED. In addition + * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: + * + * struct static_key false = STATIC_KEY_INIT_FALSE; + * struct static_key true = STATIC_KEY_INIT_TRUE; + * static_key_true() + * static_key_false() + * + * The updated API replacements are: + * + * DEFINE_STATIC_KEY_TRUE(key); + * DEFINE_STATIC_KEY_FALSE(key); + * static_branch_likely() + * static_branch_unlikely() * * Jump labels provide an interface to generate dynamic branches using - * self-modifying code. Assuming toolchain and architecture support the result - * of a "if (static_key_false(&key))" statement is a unconditional branch (which - * defaults to false - and the true block is placed out of line). - * - * However at runtime we can change the branch target using - * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key - * object and for as long as there are references all branches referring to - * that particular key will point to the (out of line) true block. + * self-modifying code. Assuming toolchain and architecture support, if we + * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", + * an "if (static_branch_unlikely(&key))" statement is an unconditional branch + * (which defaults to false - and the true block is placed out of line). + * Similarly, we can define an initially true key via + * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same + * "if (static_branch_unlikely(&key))", in which case we will generate an + * unconditional branch to the out-of-line true branch. Keys that are + * initially true or false can be using in both static_branch_unlikely() + * and static_branch_likely() statements. + * + * At runtime we can change the branch target by setting the key + * to true via a call to static_branch_enable(), or false using + * static_branch_disable(). If the direction of the branch is switched by + * these calls then we run-time modify the branch target via a + * no-op -> jump or jump -> no-op conversion. For example, for an + * initially false key that is used in an "if (static_branch_unlikely(&key))" + * statement, setting the key to true requires us to patch in a jump + * to the out-of-line of true branch. + * + * In addition to static_branch_{enable,disable}, we can also reference count + * the key or branch direction via static_branch_{inc,dec}. Thus, + * static_branch_inc() can be thought of as a 'make more true' and + * static_branch_dec() as a 'make more false'. * - * Since this relies on modifying code the static_key_slow_{inc,dec}() functions + * Since this relies on modifying code, the branch modifying functions * must be considered absolute slow paths (machine wide synchronization etc.). - * OTOH, since the affected branches are unconditional their runtime overhead + * OTOH, since the affected branches are unconditional, their runtime overhead * will be absolutely minimal, esp. in the default (off) case where the total * effect is a single NOP of appropriate size. The on case will patch in a jump * to the out-of-line block. * - * When the control is directly exposed to userspace it is prudent to delay the + * When the control is directly exposed to userspace, it is prudent to delay the * decrement to avoid high frequency code modifications which can (and do) * cause significant performance degradation. Struct static_key_deferred and * static_key_slow_dec_deferred() provide for this. * - * Lacking toolchain and or architecture support, it falls back to a simple - * conditional branch. - * - * struct static_key my_key = STATIC_KEY_INIT_TRUE; - * - * if (static_key_true(&my_key)) { - * } - * - * will result in the true case being in-line and starts the key with a single - * reference. Mixing static_key_true() and static_key_false() on the same key is not - * allowed. - * - * Not initializing the key (static data is initialized to 0s anyway) is the - * same as using STATIC_KEY_INIT_FALSE. + * Lacking toolchain and or architecture support, static keys fall back to a + * simple conditional branch. * -*/ + * Additional babbling in: Documentation/static-keys.txt + */ + +#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) +# define HAVE_JUMP_LABEL +#endif + +#ifndef __ASSEMBLY__ #include #include -#include +#include -#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) +extern bool static_key_initialized; + +#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ + "%s used before call to jump_label_init", \ + __func__) + +#ifdef HAVE_JUMP_LABEL struct static_key { atomic_t enabled; @@ -61,49 +95,52 @@ #endif }; -struct static_key_deferred { - struct static_key key; - unsigned long timeout; - struct delayed_work work; +#else +struct static_key { + atomic_t enabled; }; +#endif /* HAVE_JUMP_LABEL */ +#endif /* __ASSEMBLY__ */ -# include -# define HAVE_JUMP_LABEL -#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ +#ifdef HAVE_JUMP_LABEL +#include +#endif + +#ifndef __ASSEMBLY__ enum jump_label_type { - JUMP_LABEL_DISABLE = 0, - JUMP_LABEL_ENABLE, + JUMP_LABEL_NOP = 0, + JUMP_LABEL_JMP, }; struct module; -#ifdef HAVE_JUMP_LABEL +#include -#define JUMP_LABEL_TRUE_BRANCH 1UL +#ifdef HAVE_JUMP_LABEL -static -inline struct jump_entry *jump_label_get_entries(struct static_key *key) +static inline int static_key_count(struct static_key *key) { - return (struct jump_entry *)((unsigned long)key->entries - & ~JUMP_LABEL_TRUE_BRANCH); + /* + * -1 means the first static_key_slow_inc() is in progress. + * static_key_enabled() must return true, so return 1 here. + */ + int n = atomic_read(&key->enabled); + return n >= 0 ? n : 1; } -static inline bool jump_label_get_branch_default(struct static_key *key) -{ - if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH) - return true; - return false; -} +#define JUMP_TYPE_FALSE 0UL +#define JUMP_TYPE_TRUE 1UL +#define JUMP_TYPE_MASK 1UL static __always_inline bool static_key_false(struct static_key *key) { - return arch_static_branch(key); + return arch_static_branch(key, false); } static __always_inline bool static_key_true(struct static_key *key) { - return !static_key_false(key); + return !arch_static_branch(key, true); } extern struct jump_entry __start___jump_table[]; @@ -119,61 +156,53 @@ extern int jump_label_text_reserved(void *start, void *end); extern void static_key_slow_inc(struct static_key *key); extern void static_key_slow_dec(struct static_key *key); -extern void static_key_slow_dec_deferred(struct static_key_deferred *key); extern void jump_label_apply_nops(struct module *mod); -extern void -jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl); -#define STATIC_KEY_INIT_TRUE ((struct static_key) \ - { .enabled = ATOMIC_INIT(1), .entries = (void *)1 }) -#define STATIC_KEY_INIT_FALSE ((struct static_key) \ - { .enabled = ATOMIC_INIT(0), .entries = (void *)0 }) +#define STATIC_KEY_INIT_TRUE \ + { .enabled = ATOMIC_INIT(1), \ + .entries = (void *)JUMP_TYPE_TRUE } +#define STATIC_KEY_INIT_FALSE \ + { .enabled = ATOMIC_INIT(0), \ + .entries = (void *)JUMP_TYPE_FALSE } #else /* !HAVE_JUMP_LABEL */ -#include - -struct static_key { - atomic_t enabled; -}; +static inline int static_key_count(struct static_key *key) +{ + return atomic_read(&key->enabled); +} static __always_inline void jump_label_init(void) { + static_key_initialized = true; } -struct static_key_deferred { - struct static_key key; -}; - static __always_inline bool static_key_false(struct static_key *key) { - if (unlikely(atomic_read(&key->enabled)) > 0) + if (unlikely(static_key_count(key) > 0)) return true; return false; } static __always_inline bool static_key_true(struct static_key *key) { - if (likely(atomic_read(&key->enabled)) > 0) + if (likely(static_key_count(key) > 0)) return true; return false; } 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); } -static inline void static_key_slow_dec_deferred(struct static_key_deferred *key) -{ - static_key_slow_dec(&key->key); -} - static inline int jump_label_text_reserved(void *start, void *end) { return 0; @@ -187,30 +216,19 @@ return 0; } -static inline void -jump_label_rate_limit(struct static_key_deferred *key, - unsigned long rl) -{ -} - -#define STATIC_KEY_INIT_TRUE ((struct static_key) \ - { .enabled = ATOMIC_INIT(1) }) -#define STATIC_KEY_INIT_FALSE ((struct static_key) \ - { .enabled = ATOMIC_INIT(0) }) +#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } +#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } #endif /* HAVE_JUMP_LABEL */ #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE #define jump_label_enabled static_key_enabled -static inline bool static_key_enabled(struct static_key *key) -{ - return (atomic_read(&key->enabled) > 0); -} - static inline void static_key_enable(struct static_key *key) { - int count = atomic_read(&key->enabled); + int count = static_key_count(key); + + WARN_ON_ONCE(count < 0 || count > 1); if (!count) static_key_slow_inc(key); @@ -218,10 +236,154 @@ static inline void static_key_disable(struct static_key *key) { - int count = atomic_read(&key->enabled); + int count = static_key_count(key); + + WARN_ON_ONCE(count < 0 || count > 1); if (count) static_key_slow_dec(key); } +/* -------------------------------------------------------------------------- */ + +/* + * Two type wrappers around static_key, such that we can use compile time + * type differentiation to emit the right code. + * + * All the below code is macros in order to play type games. + */ + +struct static_key_true { + struct static_key key; +}; + +struct static_key_false { + struct static_key key; +}; + +#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } +#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } + +#define DEFINE_STATIC_KEY_TRUE(name) \ + struct static_key_true name = STATIC_KEY_TRUE_INIT + +#define DEFINE_STATIC_KEY_FALSE(name) \ + struct static_key_false name = STATIC_KEY_FALSE_INIT + +extern bool ____wrong_branch_error(void); + +#define static_key_enabled(x) \ +({ \ + if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ + !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ + !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ + ____wrong_branch_error(); \ + static_key_count((struct static_key *)x) > 0; \ +}) + +#ifdef HAVE_JUMP_LABEL + +/* + * Combine the right initial value (type) with the right branch order + * to generate the desired result. + * + * + * type\branch| likely (1) | unlikely (0) + * -----------+-----------------------+------------------ + * | | + * true (1) | ... | ... + * | NOP | JMP L + * | | 1: ... + * | L: ... | + * | | + * | | L: + * | | jmp 1b + * | | + * -----------+-----------------------+------------------ + * | | + * false (0) | ... | ... + * | JMP L | NOP + * | | 1: ... + * | L: ... | + * | | + * | | L: + * | | jmp 1b + * | | + * -----------+-----------------------+------------------ + * + * The initial value is encoded in the LSB of static_key::entries, + * type: 0 = false, 1 = true. + * + * The branch type is encoded in the LSB of jump_entry::key, + * branch: 0 = unlikely, 1 = likely. + * + * This gives the following logic table: + * + * enabled type branch instuction + * -----------------------------+----------- + * 0 0 0 | NOP + * 0 0 1 | JMP + * 0 1 0 | NOP + * 0 1 1 | JMP + * + * 1 0 0 | JMP + * 1 0 1 | NOP + * 1 1 0 | JMP + * 1 1 1 | NOP + * + * Which gives the following functions: + * + * dynamic: instruction = enabled ^ branch + * static: instruction = type ^ branch + * + * See jump_label_type() / jump_label_init_type(). + */ + +#define static_branch_likely(x) \ +({ \ + bool branch; \ + if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ + branch = !arch_static_branch(&(x)->key, true); \ + else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ + branch = !arch_static_branch_jump(&(x)->key, true); \ + else \ + branch = ____wrong_branch_error(); \ + branch; \ +}) + +#define static_branch_unlikely(x) \ +({ \ + bool branch; \ + if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ + branch = arch_static_branch_jump(&(x)->key, false); \ + else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ + branch = arch_static_branch(&(x)->key, false); \ + else \ + branch = ____wrong_branch_error(); \ + branch; \ +}) + +#else /* !HAVE_JUMP_LABEL */ + +#define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) +#define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) + +#endif /* HAVE_JUMP_LABEL */ + +/* + * Advanced usage; refcount, branch is enabled when: count != 0 + */ + +#define static_branch_inc(x) static_key_slow_inc(&(x)->key) +#define static_branch_dec(x) static_key_slow_dec(&(x)->key) + +/* + * Normal usage; boolean enable/disable. + */ + +#define static_branch_enable(x) static_key_enable(&(x)->key) +#define static_branch_disable(x) static_key_disable(&(x)->key) + #endif /* _LINUX_JUMP_LABEL_H */ + +#endif /* __ASSEMBLY__ */