cregit-Linux how code gets into the kernel

Release 4.12 include/asm-generic/barrier.h

/*
 * Generic barrier definitions, originally based on MN10300 definitions.
 *
 * It should be possible to use these on really simple architectures,
 * but it serves more as a starting point for new ports.
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#ifndef __ASM_GENERIC_BARRIER_H

#define __ASM_GENERIC_BARRIER_H

#ifndef __ASSEMBLY__

#include <linux/compiler.h>

#ifndef nop

#define nop()	asm volatile ("nop")
#endif

/*
 * Force strict CPU ordering. And yes, this is required on UP too when we're
 * talking to devices.
 *
 * Fall back to compiler barriers if nothing better is provided.
 */

#ifndef mb

#define mb()	barrier()
#endif

#ifndef rmb

#define rmb()	mb()
#endif

#ifndef wmb

#define wmb()	mb()
#endif

#ifndef dma_rmb

#define dma_rmb()	rmb()
#endif

#ifndef dma_wmb

#define dma_wmb()	wmb()
#endif

#ifndef read_barrier_depends

#define read_barrier_depends()		do { } while (0)
#endif

#ifndef __smp_mb

#define __smp_mb()	mb()
#endif

#ifndef __smp_rmb

#define __smp_rmb()	rmb()
#endif

#ifndef __smp_wmb

#define __smp_wmb()	wmb()
#endif

#ifndef __smp_read_barrier_depends

#define __smp_read_barrier_depends()	read_barrier_depends()
#endif

#ifdef CONFIG_SMP

#ifndef smp_mb

#define smp_mb()	__smp_mb()
#endif

#ifndef smp_rmb

#define smp_rmb()	__smp_rmb()
#endif

#ifndef smp_wmb

#define smp_wmb()	__smp_wmb()
#endif

#ifndef smp_read_barrier_depends

#define smp_read_barrier_depends()	__smp_read_barrier_depends()
#endif

#else	/* !CONFIG_SMP */

#ifndef smp_mb

#define smp_mb()	barrier()
#endif

#ifndef smp_rmb

#define smp_rmb()	barrier()
#endif

#ifndef smp_wmb

#define smp_wmb()	barrier()
#endif

#ifndef smp_read_barrier_depends

#define smp_read_barrier_depends()	do { } while (0)
#endif

#endif	/* CONFIG_SMP */

#ifndef __smp_store_mb

#define __smp_store_mb(var, value)  do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
#endif

#ifndef __smp_mb__before_atomic

#define __smp_mb__before_atomic()	__smp_mb()
#endif

#ifndef __smp_mb__after_atomic

#define __smp_mb__after_atomic()	__smp_mb()
#endif

#ifndef __smp_store_release

#define __smp_store_release(p, v)					\
do {                                                                    \
        compiletime_assert_atomic_type(*p);                             \
        __smp_mb();                                                     \
        WRITE_ONCE(*p, v);                                              \
} while (0)
#endif

#ifndef __smp_load_acquire

#define __smp_load_acquire(p)						\
({                                                                      \
        typeof(*p) ___p1 = READ_ONCE(*p);                               \
        compiletime_assert_atomic_type(*p);                             \
        __smp_mb();                                                     \
        ___p1;                                                          \
})
#endif

#ifdef CONFIG_SMP

#ifndef smp_store_mb

#define smp_store_mb(var, value)  __smp_store_mb(var, value)
#endif

#ifndef smp_mb__before_atomic

#define smp_mb__before_atomic()	__smp_mb__before_atomic()
#endif

#ifndef smp_mb__after_atomic

#define smp_mb__after_atomic()	__smp_mb__after_atomic()
#endif

#ifndef smp_store_release

#define smp_store_release(p, v) __smp_store_release(p, v)
#endif

#ifndef smp_load_acquire

#define smp_load_acquire(p) __smp_load_acquire(p)
#endif

#else	/* !CONFIG_SMP */

#ifndef smp_store_mb

#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); barrier(); } while (0)
#endif

#ifndef smp_mb__before_atomic

#define smp_mb__before_atomic()	barrier()
#endif

#ifndef smp_mb__after_atomic

#define smp_mb__after_atomic()	barrier()
#endif

#ifndef smp_store_release

#define smp_store_release(p, v)						\
do {                                                                    \
        compiletime_assert_atomic_type(*p);                             \
        barrier();                                                      \
        WRITE_ONCE(*p, v);                                              \
} while (0)
#endif

#ifndef smp_load_acquire

#define smp_load_acquire(p)						\
({                                                                      \
        typeof(*p) ___p1 = READ_ONCE(*p);                               \
        compiletime_assert_atomic_type(*p);                             \
        barrier();                                                      \
        ___p1;                                                          \
})
#endif

#endif	/* CONFIG_SMP */

/* Barriers for virtual machine guests when talking to an SMP host */

#define virt_mb() __smp_mb()

#define virt_rmb() __smp_rmb()

#define virt_wmb() __smp_wmb()

#define virt_read_barrier_depends() __smp_read_barrier_depends()

#define virt_store_mb(var, value) __smp_store_mb(var, value)

#define virt_mb__before_atomic() __smp_mb__before_atomic()

#define virt_mb__after_atomic()	__smp_mb__after_atomic()

#define virt_store_release(p, v) __smp_store_release(p, v)

#define virt_load_acquire(p) __smp_load_acquire(p)

/**
 * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency
 *
 * A control dependency provides a LOAD->STORE order, the additional RMB
 * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
 * aka. (load)-ACQUIRE.
 *
 * Architectures that do not do load speculation can have this be barrier().
 */
#ifndef smp_acquire__after_ctrl_dep

#define smp_acquire__after_ctrl_dep()		smp_rmb()
#endif

/**
 * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
 * @ptr: pointer to the variable to wait on
 * @cond: boolean expression to wait for
 *
 * Equivalent to using smp_load_acquire() on the condition variable but employs
 * the control dependency of the wait to reduce the barrier on many platforms.
 *
 * Due to C lacking lambda expressions we load the value of *ptr into a
 * pre-named variable @VAL to be used in @cond.
 */
#ifndef smp_cond_load_acquire

#define smp_cond_load_acquire(ptr, cond_expr) ({              \
        typeof(ptr) __PTR = (ptr);                              \
        typeof(*ptr) VAL;                                       \
        for (;;) {                                              \
                VAL = READ_ONCE(*__PTR);                        \
                if (cond_expr)                                  \
                        break;                                  \
                cpu_relax();                                    \
        }                                                       \
        smp_acquire__after_ctrl_dep();                          \
        VAL;                                                    \
})
#endif

#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */

Overall Contributors

PersonTokensPropCommitsCommitProp
Michael S. Tsirkin24549.60%323.08%
Peter Zijlstra11322.87%646.15%
David Howells7414.98%17.69%
Vineet Gupta408.10%17.69%
Alexander Duyck204.05%17.69%
Linus Torvalds20.40%17.69%
Total494100.00%13100.00%
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