Commit d84b6728 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Ingo Molnar
Browse files

locking/mcs: Better differentiate between MCS variants 



We have two flavors of the MCS spinlock: standard and cancelable (OSQ).
While each one is independent of the other, we currently mix and match
them. This patch:

  - Moves the OSQ code out of mcs_spinlock.h (which only deals with the traditional
    version) into include/linux/osq_lock.h. No unnecessary code is added to the
    more global header file, anything locks that make use of OSQ must include
    it anyway.

  - Renames mcs_spinlock.c to osq_lock.c. This file only contains osq code.

  - Introduces a CONFIG_LOCK_SPIN_ON_OWNER in order to only build osq_lock
    if there is support for it.

Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Waiman Long <Waiman.Long@hp.com>
Link: http://lkml.kernel.org/r/1420573509-24774-5-git-send-email-dave@stgolabs.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 4bd19084

include/linux/osq_lock.h

+10 −2
Original line number Diff line number Diff line
@@ -5,8 +5,11 @@ 
 * An MCS like lock especially tailored for optimistic spinning for sleeping

 * lock implementations (mutex, rwsem, etc).

 */



#define OSQ_UNLOCKED_VAL (0)

struct optimistic_spin_node {

	struct optimistic_spin_node *next, *prev;

	int locked; /* 1 if lock acquired */

	int cpu; /* encoded CPU # + 1 value */

};



struct optimistic_spin_queue {

	/*
@@ -16,6 +19,8 @@ struct optimistic_spin_queue { 
	atomic_t tail;

};



#define OSQ_UNLOCKED_VAL (0)



/* Init macro and function. */

#define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
@@ -24,4 +29,7 @@ static inline void osq_lock_init(struct optimistic_spin_queue *lock) 
	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);

}



extern bool osq_lock(struct optimistic_spin_queue *lock);

extern void osq_unlock(struct optimistic_spin_queue *lock);



#endif

kernel/Kconfig.locks

+4 −0
Original line number Diff line number Diff line
@@ -231,6 +231,10 @@ config RWSEM_SPIN_ON_OWNER 
       def_bool y

       depends on SMP && RWSEM_XCHGADD_ALGORITHM && ARCH_SUPPORTS_ATOMIC_RMW



config LOCK_SPIN_ON_OWNER

       def_bool y

       depends on MUTEX_SPIN_ON_OWNER || RWSEM_SPIN_ON_OWNER



config ARCH_USE_QUEUE_RWLOCK

	bool

kernel/locking/Makefile

+2 −1
Original line number Diff line number Diff line 


obj-y += mutex.o semaphore.o rwsem.o mcs_spinlock.o

obj-y += mutex.o semaphore.o rwsem.o



ifdef CONFIG_FUNCTION_TRACER

CFLAGS_REMOVE_lockdep.o = -pg
@@ -14,6 +14,7 @@ ifeq ($(CONFIG_PROC_FS),y) 
obj-$(CONFIG_LOCKDEP) += lockdep_proc.o

endif

obj-$(CONFIG_SMP) += spinlock.o

obj-$(CONFIG_LOCK_SPIN_ON_OWNER) += osq_lock.o

obj-$(CONFIG_SMP) += lglock.o

obj-$(CONFIG_PROVE_LOCKING) += spinlock.o

obj-$(CONFIG_RT_MUTEXES) += rtmutex.o

kernel/locking/mcs_spinlock.h

+0 −16
Original line number Diff line number Diff line
@@ -108,20 +108,4 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) 
	arch_mcs_spin_unlock_contended(&next->locked);

}



/*

 * Cancellable version of the MCS lock above.

 *

 * Intended for adaptive spinning of sleeping locks:

 * mutex_lock()/rwsem_down_{read,write}() etc.

 */



struct optimistic_spin_node {

	struct optimistic_spin_node *next, *prev;

	int locked; /* 1 if lock acquired */

	int cpu; /* encoded CPU # value */

};



extern bool osq_lock(struct optimistic_spin_queue *lock);

extern void osq_unlock(struct optimistic_spin_queue *lock);



#endif /* __LINUX_MCS_SPINLOCK_H */

kernel/locking/mcs_spinlock.c→kernel/locking/osq_lock.c

+1 −6
Original line number Diff line number Diff line 
#include <linux/percpu.h>

#include <linux/sched.h>

#include "mcs_spinlock.h"



#ifdef CONFIG_SMP

#include <linux/osq_lock.h>



/*

 * An MCS like lock especially tailored for optimistic spinning for sleeping
@@ -203,6 +201,3 @@ void osq_unlock(struct optimistic_spin_queue *lock) 
	if (next)

		ACCESS_ONCE(next->locked) = 1;

}
 


#endif

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