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![Jason Baron](/assets/img/avatar_default.png)
In the jump label enabled case, calling static_key_enabled() results in a function call. The function returns the results of a compare, so it really doesn't need the overhead of a full function call. Let's make it 'static inline' for both the jump label enabled and disabled cases. Signed-off-by: Jason Baron <jbaron@redhat.com> Cc: a.p.zijlstra@chello.nl Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@polymtl.ca Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/201202281849.q1SIn1p2023270@int-mx10.intmail.prod.int.phx2.redhat.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
226 lines
6.2 KiB
C
226 lines
6.2 KiB
C
#ifndef _LINUX_JUMP_LABEL_H
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#define _LINUX_JUMP_LABEL_H
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/*
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* Jump label support
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*
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* Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
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* Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
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*
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* Jump labels provide an interface to generate dynamic branches using
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* self-modifying code. Assuming toolchain and architecture support the result
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* of a "if (static_key_false(&key))" statement is a unconditional branch (which
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* defaults to false - and the true block is placed out of line).
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*
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* However at runtime we can change the branch target using
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* static_key_slow_{inc,dec}(). These function as a 'reference' count on the key
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* object and for as long as there are references all branches referring to
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* that particular key will point to the (out of line) true block.
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*
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* Since this relies on modifying code the static_key_slow_{inc,dec}() functions
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* must be considered absolute slow paths (machine wide synchronization etc.).
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* OTOH, since the affected branches are unconditional their runtime overhead
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* will be absolutely minimal, esp. in the default (off) case where the total
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* effect is a single NOP of appropriate size. The on case will patch in a jump
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* to the out-of-line block.
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*
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* When the control is directly exposed to userspace it is prudent to delay the
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* decrement to avoid high frequency code modifications which can (and do)
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* cause significant performance degradation. Struct static_key_deferred and
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* static_key_slow_dec_deferred() provide for this.
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*
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* Lacking toolchain and or architecture support, it falls back to a simple
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* conditional branch.
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*
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* struct static_key my_key = STATIC_KEY_INIT_TRUE;
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*
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* if (static_key_true(&my_key)) {
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* }
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*
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* will result in the true case being in-line and starts the key with a single
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* reference. Mixing static_key_true() and static_key_false() on the same key is not
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* allowed.
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*
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* Not initializing the key (static data is initialized to 0s anyway) is the
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* same as using STATIC_KEY_INIT_FALSE and static_key_false() is
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* equivalent with static_branch().
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*
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*/
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#include <linux/types.h>
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#include <linux/compiler.h>
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#include <linux/workqueue.h>
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#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
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struct static_key {
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atomic_t enabled;
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/* Set lsb bit to 1 if branch is default true, 0 ot */
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struct jump_entry *entries;
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#ifdef CONFIG_MODULES
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struct static_key_mod *next;
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#endif
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};
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struct static_key_deferred {
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struct static_key key;
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unsigned long timeout;
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struct delayed_work work;
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};
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# include <asm/jump_label.h>
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# define HAVE_JUMP_LABEL
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#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
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enum jump_label_type {
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JUMP_LABEL_DISABLE = 0,
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JUMP_LABEL_ENABLE,
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};
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struct module;
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#ifdef HAVE_JUMP_LABEL
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#define JUMP_LABEL_TRUE_BRANCH 1UL
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static
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inline struct jump_entry *jump_label_get_entries(struct static_key *key)
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{
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return (struct jump_entry *)((unsigned long)key->entries
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& ~JUMP_LABEL_TRUE_BRANCH);
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}
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static inline bool jump_label_get_branch_default(struct static_key *key)
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{
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if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH)
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return true;
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return false;
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}
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static __always_inline bool static_key_false(struct static_key *key)
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{
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return arch_static_branch(key);
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}
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static __always_inline bool static_key_true(struct static_key *key)
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{
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return !static_key_false(key);
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}
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/* Deprecated. Please use 'static_key_false() instead. */
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static __always_inline bool static_branch(struct static_key *key)
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{
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return arch_static_branch(key);
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}
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extern struct jump_entry __start___jump_table[];
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extern struct jump_entry __stop___jump_table[];
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extern void jump_label_init(void);
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extern void jump_label_lock(void);
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extern void jump_label_unlock(void);
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extern void arch_jump_label_transform(struct jump_entry *entry,
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enum jump_label_type type);
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extern void arch_jump_label_transform_static(struct jump_entry *entry,
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enum jump_label_type type);
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extern int jump_label_text_reserved(void *start, void *end);
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extern void static_key_slow_inc(struct static_key *key);
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extern void static_key_slow_dec(struct static_key *key);
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extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
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extern void jump_label_apply_nops(struct module *mod);
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extern void
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jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
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#define STATIC_KEY_INIT_TRUE ((struct static_key) \
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{ .enabled = ATOMIC_INIT(1), .entries = (void *)1 })
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#define STATIC_KEY_INIT_FALSE ((struct static_key) \
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{ .enabled = ATOMIC_INIT(0), .entries = (void *)0 })
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#else /* !HAVE_JUMP_LABEL */
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#include <linux/atomic.h>
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struct static_key {
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atomic_t enabled;
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};
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static __always_inline void jump_label_init(void)
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{
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}
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struct static_key_deferred {
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struct static_key key;
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};
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static __always_inline bool static_key_false(struct static_key *key)
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{
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if (unlikely(atomic_read(&key->enabled)) > 0)
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return true;
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return false;
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}
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static __always_inline bool static_key_true(struct static_key *key)
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{
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if (likely(atomic_read(&key->enabled)) > 0)
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return true;
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return false;
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}
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/* Deprecated. Please use 'static_key_false() instead. */
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static __always_inline bool static_branch(struct static_key *key)
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{
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if (unlikely(atomic_read(&key->enabled)) > 0)
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return true;
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return false;
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}
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static inline void static_key_slow_inc(struct static_key *key)
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{
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atomic_inc(&key->enabled);
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}
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static inline void static_key_slow_dec(struct static_key *key)
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{
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atomic_dec(&key->enabled);
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}
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static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
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{
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static_key_slow_dec(&key->key);
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}
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static inline int jump_label_text_reserved(void *start, void *end)
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{
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return 0;
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}
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static inline void jump_label_lock(void) {}
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static inline void jump_label_unlock(void) {}
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static inline int jump_label_apply_nops(struct module *mod)
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{
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return 0;
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}
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static inline void
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jump_label_rate_limit(struct static_key_deferred *key,
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unsigned long rl)
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{
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}
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#define STATIC_KEY_INIT_TRUE ((struct static_key) \
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{ .enabled = ATOMIC_INIT(1) })
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#define STATIC_KEY_INIT_FALSE ((struct static_key) \
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{ .enabled = ATOMIC_INIT(0) })
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#endif /* HAVE_JUMP_LABEL */
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#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
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#define jump_label_enabled static_key_enabled
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static inline bool static_key_enabled(struct static_key *key)
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{
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return (atomic_read(&key->enabled) > 0);
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}
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#endif /* _LINUX_JUMP_LABEL_H */
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