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Commit e3b22bc3 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull locking fix from Thomas Gleixner:
 "A single fix to address a race in the static key logic"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/static_key: Fix concurrent static_key_slow_inc()
parents 2de23071 4c5ea0a9

include/linux/jump_label.h

+13 −3
Original line number Diff line number Diff line
@@ -117,13 +117,18 @@ struct module; 


#include <linux/atomic.h>



#ifdef HAVE_JUMP_LABEL



static inline int static_key_count(struct static_key *key)

{

	return atomic_read(&key->enabled);

	/*

	 * -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;

}



#ifdef HAVE_JUMP_LABEL



#define JUMP_TYPE_FALSE	0UL

#define JUMP_TYPE_TRUE	1UL

#define JUMP_TYPE_MASK	1UL
@@ -162,6 +167,11 @@ extern void jump_label_apply_nops(struct module *mod); 


#else  /* !HAVE_JUMP_LABEL */



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;

kernel/jump_label.c

+33 −3
Original line number Diff line number Diff line
@@ -58,13 +58,36 @@ static void jump_label_update(struct static_key *key); 


void static_key_slow_inc(struct static_key *key)

{

	int v, v1;



	STATIC_KEY_CHECK_USE();

	if (atomic_inc_not_zero(&key->enabled))



	/*

	 * Careful if we get concurrent static_key_slow_inc() calls;

	 * later calls must wait for the first one to _finish_ the

	 * jump_label_update() process.  At the same time, however,

	 * the jump_label_update() call below wants to see

	 * static_key_enabled(&key) for jumps to be updated properly.

	 *

	 * So give a special meaning to negative key->enabled: it sends

	 * static_key_slow_inc() down the slow path, and it is non-zero

	 * so it counts as "enabled" in jump_label_update().  Note that

	 * atomic_inc_unless_negative() checks >= 0, so roll our own.

	 */

	for (v = atomic_read(&key->enabled); v > 0; v = v1) {

		v1 = atomic_cmpxchg(&key->enabled, v, v + 1);

		if (likely(v1 == v))

			return;

	}



	jump_label_lock();

	if (atomic_inc_return(&key->enabled) == 1)

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

		atomic_set(&key->enabled, -1);

		jump_label_update(key);

		atomic_set(&key->enabled, 1);

	} else {

		atomic_inc(&key->enabled);

	}

	jump_label_unlock();

}

EXPORT_SYMBOL_GPL(static_key_slow_inc);
@@ -72,6 +95,13 @@ EXPORT_SYMBOL_GPL(static_key_slow_inc); 
static void __static_key_slow_dec(struct static_key *key,

		unsigned long rate_limit, struct delayed_work *work)

{

	/*

	 * The negative count check is valid even when a negative

	 * key->enabled is in use by static_key_slow_inc(); a

	 * __static_key_slow_dec() before the first static_key_slow_inc()

	 * returns is unbalanced, because all other static_key_slow_inc()

	 * instances block while the update is in progress.

	 */

	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {

		WARN(atomic_read(&key->enabled) < 0,

		     "jump label: negative count!\n");