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![Paul E. McKenney](/assets/img/avatar_default.png)
The Linux kernel has traditionally required that an UNLOCK+LOCK pair act as a full memory barrier when either (1) that UNLOCK+LOCK pair was executed by the same CPU or task, or (2) the same lock variable was used for the UNLOCK and LOCK. It now seems likely that very few places in the kernel rely on this full-memory-barrier semantic, and with the advent of queued locks, providing this semantic either requires complex reasoning, or for some architectures, added overhead. This commit therefore adds a smp_mb__after_unlock_lock(), which may be placed after a LOCK primitive to restore the full-memory-barrier semantic. All definitions are currently no-ops, but will be upgraded for some architectures when queued locks arrive. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <linux-arch@vger.kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1386799151-2219-5-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
415 lines
11 KiB
C
415 lines
11 KiB
C
#ifndef __LINUX_SPINLOCK_H
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#define __LINUX_SPINLOCK_H
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/*
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* include/linux/spinlock.h - generic spinlock/rwlock declarations
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*
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* here's the role of the various spinlock/rwlock related include files:
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*
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* on SMP builds:
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*
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* asm/spinlock_types.h: contains the arch_spinlock_t/arch_rwlock_t and the
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* initializers
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*
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* linux/spinlock_types.h:
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* defines the generic type and initializers
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*
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* asm/spinlock.h: contains the arch_spin_*()/etc. lowlevel
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* implementations, mostly inline assembly code
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*
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* (also included on UP-debug builds:)
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*
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* linux/spinlock_api_smp.h:
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* contains the prototypes for the _spin_*() APIs.
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*
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* linux/spinlock.h: builds the final spin_*() APIs.
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*
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* on UP builds:
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*
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* linux/spinlock_type_up.h:
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* contains the generic, simplified UP spinlock type.
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* (which is an empty structure on non-debug builds)
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*
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* linux/spinlock_types.h:
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* defines the generic type and initializers
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*
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* linux/spinlock_up.h:
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* contains the arch_spin_*()/etc. version of UP
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* builds. (which are NOPs on non-debug, non-preempt
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* builds)
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*
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* (included on UP-non-debug builds:)
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*
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* linux/spinlock_api_up.h:
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* builds the _spin_*() APIs.
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*
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* linux/spinlock.h: builds the final spin_*() APIs.
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*/
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#include <linux/typecheck.h>
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#include <linux/preempt.h>
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#include <linux/linkage.h>
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#include <linux/compiler.h>
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#include <linux/irqflags.h>
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#include <linux/thread_info.h>
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#include <linux/kernel.h>
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#include <linux/stringify.h>
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#include <linux/bottom_half.h>
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#include <asm/barrier.h>
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/*
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* Must define these before including other files, inline functions need them
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*/
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#define LOCK_SECTION_NAME ".text..lock."KBUILD_BASENAME
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#define LOCK_SECTION_START(extra) \
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".subsection 1\n\t" \
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extra \
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".ifndef " LOCK_SECTION_NAME "\n\t" \
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LOCK_SECTION_NAME ":\n\t" \
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".endif\n"
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#define LOCK_SECTION_END \
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".previous\n\t"
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#define __lockfunc __attribute__((section(".spinlock.text")))
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/*
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* Pull the arch_spinlock_t and arch_rwlock_t definitions:
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*/
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#include <linux/spinlock_types.h>
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/*
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* Pull the arch_spin*() functions/declarations (UP-nondebug doesn't need them):
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*/
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#ifdef CONFIG_SMP
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# include <asm/spinlock.h>
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#else
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# include <linux/spinlock_up.h>
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#endif
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#ifdef CONFIG_DEBUG_SPINLOCK
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extern void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
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struct lock_class_key *key);
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# define raw_spin_lock_init(lock) \
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do { \
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static struct lock_class_key __key; \
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\
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__raw_spin_lock_init((lock), #lock, &__key); \
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} while (0)
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#else
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# define raw_spin_lock_init(lock) \
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do { *(lock) = __RAW_SPIN_LOCK_UNLOCKED(lock); } while (0)
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#endif
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#define raw_spin_is_locked(lock) arch_spin_is_locked(&(lock)->raw_lock)
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#ifdef CONFIG_GENERIC_LOCKBREAK
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#define raw_spin_is_contended(lock) ((lock)->break_lock)
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#else
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#ifdef arch_spin_is_contended
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#define raw_spin_is_contended(lock) arch_spin_is_contended(&(lock)->raw_lock)
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#else
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#define raw_spin_is_contended(lock) (((void)(lock), 0))
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#endif /*arch_spin_is_contended*/
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#endif
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/*
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* Despite its name it doesn't necessarily has to be a full barrier.
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* It should only guarantee that a STORE before the critical section
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* can not be reordered with a LOAD inside this section.
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* spin_lock() is the one-way barrier, this LOAD can not escape out
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* of the region. So the default implementation simply ensures that
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* a STORE can not move into the critical section, smp_wmb() should
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* serialize it with another STORE done by spin_lock().
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*/
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#ifndef smp_mb__before_spinlock
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#define smp_mb__before_spinlock() smp_wmb()
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#endif
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/*
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* Place this after a lock-acquisition primitive to guarantee that
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* an UNLOCK+LOCK pair act as a full barrier. This guarantee applies
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* if the UNLOCK and LOCK are executed by the same CPU or if the
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* UNLOCK and LOCK operate on the same lock variable.
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*/
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#ifndef smp_mb__after_unlock_lock
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#define smp_mb__after_unlock_lock() do { } while (0)
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#endif
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/**
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* raw_spin_unlock_wait - wait until the spinlock gets unlocked
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* @lock: the spinlock in question.
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*/
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#define raw_spin_unlock_wait(lock) arch_spin_unlock_wait(&(lock)->raw_lock)
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#ifdef CONFIG_DEBUG_SPINLOCK
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extern void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock);
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#define do_raw_spin_lock_flags(lock, flags) do_raw_spin_lock(lock)
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extern int do_raw_spin_trylock(raw_spinlock_t *lock);
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extern void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock);
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#else
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static inline void do_raw_spin_lock(raw_spinlock_t *lock) __acquires(lock)
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{
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__acquire(lock);
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arch_spin_lock(&lock->raw_lock);
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}
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static inline void
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do_raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long *flags) __acquires(lock)
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{
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__acquire(lock);
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arch_spin_lock_flags(&lock->raw_lock, *flags);
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}
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static inline int do_raw_spin_trylock(raw_spinlock_t *lock)
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{
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return arch_spin_trylock(&(lock)->raw_lock);
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}
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static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
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{
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arch_spin_unlock(&lock->raw_lock);
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__release(lock);
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}
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#endif
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/*
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* Define the various spin_lock methods. Note we define these
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* regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The
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* various methods are defined as nops in the case they are not
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* required.
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*/
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#define raw_spin_trylock(lock) __cond_lock(lock, _raw_spin_trylock(lock))
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#define raw_spin_lock(lock) _raw_spin_lock(lock)
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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# define raw_spin_lock_nested(lock, subclass) \
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_raw_spin_lock_nested(lock, subclass)
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# define raw_spin_lock_nest_lock(lock, nest_lock) \
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do { \
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typecheck(struct lockdep_map *, &(nest_lock)->dep_map);\
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_raw_spin_lock_nest_lock(lock, &(nest_lock)->dep_map); \
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} while (0)
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#else
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# define raw_spin_lock_nested(lock, subclass) _raw_spin_lock(lock)
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# define raw_spin_lock_nest_lock(lock, nest_lock) _raw_spin_lock(lock)
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#endif
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#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
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#define raw_spin_lock_irqsave(lock, flags) \
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do { \
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typecheck(unsigned long, flags); \
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flags = _raw_spin_lock_irqsave(lock); \
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} while (0)
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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#define raw_spin_lock_irqsave_nested(lock, flags, subclass) \
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do { \
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typecheck(unsigned long, flags); \
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flags = _raw_spin_lock_irqsave_nested(lock, subclass); \
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} while (0)
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#else
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#define raw_spin_lock_irqsave_nested(lock, flags, subclass) \
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do { \
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typecheck(unsigned long, flags); \
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flags = _raw_spin_lock_irqsave(lock); \
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} while (0)
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#endif
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#else
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#define raw_spin_lock_irqsave(lock, flags) \
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do { \
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typecheck(unsigned long, flags); \
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_raw_spin_lock_irqsave(lock, flags); \
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} while (0)
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#define raw_spin_lock_irqsave_nested(lock, flags, subclass) \
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raw_spin_lock_irqsave(lock, flags)
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#endif
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#define raw_spin_lock_irq(lock) _raw_spin_lock_irq(lock)
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#define raw_spin_lock_bh(lock) _raw_spin_lock_bh(lock)
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#define raw_spin_unlock(lock) _raw_spin_unlock(lock)
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#define raw_spin_unlock_irq(lock) _raw_spin_unlock_irq(lock)
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#define raw_spin_unlock_irqrestore(lock, flags) \
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do { \
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typecheck(unsigned long, flags); \
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_raw_spin_unlock_irqrestore(lock, flags); \
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} while (0)
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#define raw_spin_unlock_bh(lock) _raw_spin_unlock_bh(lock)
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#define raw_spin_trylock_bh(lock) \
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__cond_lock(lock, _raw_spin_trylock_bh(lock))
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#define raw_spin_trylock_irq(lock) \
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({ \
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local_irq_disable(); \
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raw_spin_trylock(lock) ? \
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1 : ({ local_irq_enable(); 0; }); \
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})
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#define raw_spin_trylock_irqsave(lock, flags) \
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({ \
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local_irq_save(flags); \
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raw_spin_trylock(lock) ? \
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1 : ({ local_irq_restore(flags); 0; }); \
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})
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/**
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* raw_spin_can_lock - would raw_spin_trylock() succeed?
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* @lock: the spinlock in question.
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*/
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#define raw_spin_can_lock(lock) (!raw_spin_is_locked(lock))
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/* Include rwlock functions */
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#include <linux/rwlock.h>
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/*
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* Pull the _spin_*()/_read_*()/_write_*() functions/declarations:
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*/
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#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
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# include <linux/spinlock_api_smp.h>
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#else
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# include <linux/spinlock_api_up.h>
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#endif
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/*
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* Map the spin_lock functions to the raw variants for PREEMPT_RT=n
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*/
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static inline raw_spinlock_t *spinlock_check(spinlock_t *lock)
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{
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return &lock->rlock;
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}
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#define spin_lock_init(_lock) \
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do { \
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spinlock_check(_lock); \
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raw_spin_lock_init(&(_lock)->rlock); \
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} while (0)
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static inline void spin_lock(spinlock_t *lock)
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{
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raw_spin_lock(&lock->rlock);
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}
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static inline void spin_lock_bh(spinlock_t *lock)
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{
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raw_spin_lock_bh(&lock->rlock);
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}
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static inline int spin_trylock(spinlock_t *lock)
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{
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return raw_spin_trylock(&lock->rlock);
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}
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#define spin_lock_nested(lock, subclass) \
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do { \
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raw_spin_lock_nested(spinlock_check(lock), subclass); \
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} while (0)
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#define spin_lock_nest_lock(lock, nest_lock) \
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do { \
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raw_spin_lock_nest_lock(spinlock_check(lock), nest_lock); \
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} while (0)
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static inline void spin_lock_irq(spinlock_t *lock)
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{
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raw_spin_lock_irq(&lock->rlock);
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}
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#define spin_lock_irqsave(lock, flags) \
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do { \
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raw_spin_lock_irqsave(spinlock_check(lock), flags); \
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} while (0)
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#define spin_lock_irqsave_nested(lock, flags, subclass) \
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do { \
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raw_spin_lock_irqsave_nested(spinlock_check(lock), flags, subclass); \
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} while (0)
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static inline void spin_unlock(spinlock_t *lock)
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{
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raw_spin_unlock(&lock->rlock);
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}
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static inline void spin_unlock_bh(spinlock_t *lock)
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{
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raw_spin_unlock_bh(&lock->rlock);
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}
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static inline void spin_unlock_irq(spinlock_t *lock)
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{
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raw_spin_unlock_irq(&lock->rlock);
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}
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static inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
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{
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raw_spin_unlock_irqrestore(&lock->rlock, flags);
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}
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static inline int spin_trylock_bh(spinlock_t *lock)
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{
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return raw_spin_trylock_bh(&lock->rlock);
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}
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static inline int spin_trylock_irq(spinlock_t *lock)
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{
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return raw_spin_trylock_irq(&lock->rlock);
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}
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#define spin_trylock_irqsave(lock, flags) \
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({ \
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raw_spin_trylock_irqsave(spinlock_check(lock), flags); \
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})
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static inline void spin_unlock_wait(spinlock_t *lock)
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{
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raw_spin_unlock_wait(&lock->rlock);
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}
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static inline int spin_is_locked(spinlock_t *lock)
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{
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return raw_spin_is_locked(&lock->rlock);
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}
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static inline int spin_is_contended(spinlock_t *lock)
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{
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return raw_spin_is_contended(&lock->rlock);
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}
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static inline int spin_can_lock(spinlock_t *lock)
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{
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return raw_spin_can_lock(&lock->rlock);
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}
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#define assert_spin_locked(lock) assert_raw_spin_locked(&(lock)->rlock)
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/*
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* Pull the atomic_t declaration:
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* (asm-mips/atomic.h needs above definitions)
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*/
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#include <linux/atomic.h>
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/**
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* atomic_dec_and_lock - lock on reaching reference count zero
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* @atomic: the atomic counter
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* @lock: the spinlock in question
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*
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* Decrements @atomic by 1. If the result is 0, returns true and locks
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* @lock. Returns false for all other cases.
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*/
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extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
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#define atomic_dec_and_lock(atomic, lock) \
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__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))
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#endif /* __LINUX_SPINLOCK_H */
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