• M
    locking/atomics: Switch to generated fallbacks · 9fa45070
    Mark Rutland 提交于
    As a step to ensuring the atomic* APIs are consistent, switch to fallbacks
    generated by gen-atomic-fallback.sh.
    
    These are checked in rather than generated with Kbuild, since:
    
    * This allows inspection of the atomics with git grep and ctags on a
      pristine tree, which Linus strongly prefers being able to do.
    
    * The fallbacks are not affected by machine details or configuration
      options, so it is not necessary to regenerate them to take these into
      account.
    
    * These are included by files required *very* early in the build process
      (e.g. for generating bounds.h), and we'd rather not complicate the
      top-level Kbuild file with dependencies.
    
    The new fallback header should be equivalent to the old fallbacks in
    <linux/atomic.h>, but:
    
    * It is formatted a little differently due to scripting ensuring things
      are more regular than they used to be.
    
    * Fallbacks are now expanded in-place as static inline functions rather
      than macros.
    
    * The prototypes for fallbacks are arragned consistently with the return
      type on a separate line to try to keep to a sensible line length.
    
    There should be no functional change as a result of this patch.
    Signed-off-by: NMark Rutland <mark.rutland@arm.com>
    Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: NWill Deacon <will.deacon@arm.com>
    Cc: linux-arm-kernel@lists.infradead.org
    Cc: catalin.marinas@arm.com
    Cc: linuxdrivers@attotech.com
    Cc: dvyukov@google.com
    Cc: Boqun Feng <boqun.feng@gmail.com>
    Cc: arnd@arndb.de
    Cc: aryabinin@virtuozzo.com
    Cc: glider@google.com
    Link: http://lkml.kernel.org/r/20180904104830.2975-3-mark.rutland@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
    9fa45070
atomic.h 2.2 KB
/* SPDX-License-Identifier: GPL-2.0 */
/* Atomic operations usable in machine independent code */
#ifndef _LINUX_ATOMIC_H
#define _LINUX_ATOMIC_H
#include <linux/types.h>

#include <asm/atomic.h>
#include <asm/barrier.h>

/*
 * Relaxed variants of xchg, cmpxchg and some atomic operations.
 *
 * We support four variants:
 *
 * - Fully ordered: The default implementation, no suffix required.
 * - Acquire: Provides ACQUIRE semantics, _acquire suffix.
 * - Release: Provides RELEASE semantics, _release suffix.
 * - Relaxed: No ordering guarantees, _relaxed suffix.
 *
 * For compound atomics performing both a load and a store, ACQUIRE
 * semantics apply only to the load and RELEASE semantics only to the
 * store portion of the operation. Note that a failed cmpxchg_acquire
 * does -not- imply any memory ordering constraints.
 *
 * See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions.
 */

/*
 * The idea here is to build acquire/release variants by adding explicit
 * barriers on top of the relaxed variant. In the case where the relaxed
 * variant is already fully ordered, no additional barriers are needed.
 *
 * If an architecture overrides __atomic_acquire_fence() it will probably
 * want to define smp_mb__after_spinlock().
 */
#ifndef __atomic_acquire_fence
#define __atomic_acquire_fence		smp_mb__after_atomic
#endif

#ifndef __atomic_release_fence
#define __atomic_release_fence		smp_mb__before_atomic
#endif

#ifndef __atomic_pre_full_fence
#define __atomic_pre_full_fence		smp_mb__before_atomic
#endif

#ifndef __atomic_post_full_fence
#define __atomic_post_full_fence	smp_mb__after_atomic
#endif

#define __atomic_op_acquire(op, args...)				\
({									\
	typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);		\
	__atomic_acquire_fence();					\
	__ret;								\
})

#define __atomic_op_release(op, args...)				\
({									\
	__atomic_release_fence();					\
	op##_relaxed(args);						\
})

#define __atomic_op_fence(op, args...)					\
({									\
	typeof(op##_relaxed(args)) __ret;				\
	__atomic_pre_full_fence();					\
	__ret = op##_relaxed(args);					\
	__atomic_post_full_fence();					\
	__ret;								\
})

#include <linux/atomic-fallback.h>

#include <asm-generic/atomic-long.h>

#endif /* _LINUX_ATOMIC_H */
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