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Commit 5a40527f authored by Marc Zyngier's avatar Marc Zyngier Committed by Ingo Molnar
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jump_label: Provide hotplug context variants 



As using the normal static key API under the hotplug lock is
pretty much impossible, let's provide a variant of some of them
that require the hotplug lock to have already been taken.

These function are only meant to be used in CPU hotplug callbacks.

Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20170801080257.5056-4-marc.zyngier@arm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 8b7b4128

Documentation/static-keys.txt

+15 −0
Original line number Diff line number Diff line
@@ -154,6 +154,21 @@ and 'static_key_count()'. In general, if you use these functions, they 
should be protected with the same mutex used around the enable/disable

or increment/decrement function.



Note that switching branches results in some locks being taken,

particularly the CPU hotplug lock (in order to avoid races against

CPUs being brought in the kernel whilst the kernel is getting

patched). Calling the static key API from within a hotplug notifier is

thus a sure deadlock recipe. In order to still allow use of the

functionnality, the following functions are provided:



	static_key_enable_cpuslocked()

	static_key_disable_cpuslocked()

	static_branch_enable_cpuslocked()

	static_branch_disable_cpuslocked()



These functions are *not* general purpose, and must only be used when

you really know that you're in the above context, and no other.



Where an array of keys is required, it can be defined as::



	DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);

include/linux/jump_label.h

+9 −2
Original line number Diff line number Diff line
@@ -163,6 +163,8 @@ extern void jump_label_apply_nops(struct module *mod); 
extern int static_key_count(struct static_key *key);

extern void static_key_enable(struct static_key *key);

extern void static_key_disable(struct static_key *key);

extern void static_key_enable_cpuslocked(struct static_key *key);

extern void static_key_disable_cpuslocked(struct static_key *key);



/*

 * We should be using ATOMIC_INIT() for initializing .enabled, but
@@ -254,6 +256,9 @@ static inline void static_key_disable(struct static_key *key) 
	atomic_set(&key->enabled, 0);

}



#define static_key_enable_cpuslocked(k)		static_key_enable((k))

#define static_key_disable_cpuslocked(k)	static_key_disable((k))



#define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }

#define STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
@@ -417,6 +422,8 @@ extern bool ____wrong_branch_error(void); 


#define static_branch_enable(x)			static_key_enable(&(x)->key)

#define static_branch_disable(x)		static_key_disable(&(x)->key)

#define static_branch_enable_cpuslocked(x)	static_key_enable_cpuslocked(&(x)->key)

#define static_branch_disable_cpuslocked(x)	static_key_disable_cpuslocked(&(x)->key)



#endif /* __ASSEMBLY__ */

kernel/jump_label.c

+18 −4
Original line number Diff line number Diff line
@@ -126,15 +126,15 @@ void static_key_slow_inc(struct static_key *key) 
}

EXPORT_SYMBOL_GPL(static_key_slow_inc);



void static_key_enable(struct static_key *key)

void static_key_enable_cpuslocked(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();



	if (atomic_read(&key->enabled) > 0) {

		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);

		return;

	}



	cpus_read_lock();

	jump_label_lock();

	if (atomic_read(&key->enabled) == 0) {

		atomic_set(&key->enabled, -1);
@@ -145,23 +145,37 @@ void static_key_enable(struct static_key *key) 
		atomic_set_release(&key->enabled, 1);

	}

	jump_label_unlock();

}

EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked);



void static_key_enable(struct static_key *key)

{

	cpus_read_lock();

	static_key_enable_cpuslocked(key);

	cpus_read_unlock();

}

EXPORT_SYMBOL_GPL(static_key_enable);



void static_key_disable(struct static_key *key)

void static_key_disable_cpuslocked(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();



	if (atomic_read(&key->enabled) != 1) {

		WARN_ON_ONCE(atomic_read(&key->enabled) != 0);

		return;

	}



	cpus_read_lock();

	jump_label_lock();

	if (atomic_cmpxchg(&key->enabled, 1, 0))

		jump_label_update(key);

	jump_label_unlock();

}

EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked);



void static_key_disable(struct static_key *key)

{

	cpus_read_lock();

	static_key_disable_cpuslocked(key);

	cpus_read_unlock();

}

EXPORT_SYMBOL_GPL(static_key_disable);