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linux-next/include/linux/jump_label_ratelimit.h
Hannes Frederic Sowa c4b2c0c5f6 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 <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
2013-10-19 19:45:35 -04:00

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C

#ifndef _LINUX_JUMP_LABEL_RATELIMIT_H
#define _LINUX_JUMP_LABEL_RATELIMIT_H
#include <linux/jump_label.h>
#include <linux/workqueue.h>
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
struct static_key_deferred {
struct static_key key;
unsigned long timeout;
struct delayed_work work;
};
#endif
#ifdef HAVE_JUMP_LABEL
extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
extern void
jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
#else /* !HAVE_JUMP_LABEL */
struct static_key_deferred {
struct static_key key;
};
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 */