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    Subject[PATCH v5 3/4] MCS Lock: Move mcs_lock/unlock function into its own file
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    Date
    From: Waiman Long <Waiman.Long@hp.com>

    The following changes are made:

    1) Create a new mcs_spinlock.c file to contain the
    mcs_spin_lock() and mcs_spin_unlock() function.
    2) Include a number of prerequisite header files and define
    arch_mutex_cpu_relax(), if not previously defined so the
    mcs functions can be compiled for multiple architecture without
    causing problems.

    Signed-off-by: Waiman Long <Waiman.Long@hp.com>
    Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
    ---
    include/linux/mcs_spinlock.h | 56 ++------------------
    kernel/locking/Makefile | 6 +-
    .../locking/mcs_spinlock.c | 31 ++++++-----
    3 files changed, 23 insertions(+), 70 deletions(-)
    copy include/linux/mcs_spinlock.h => kernel/locking/mcs_spinlock.c (78%)

    diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h
    index 96f14299..d54bb23 100644
    --- a/include/linux/mcs_spinlock.h
    +++ b/include/linux/mcs_spinlock.h
    @@ -17,57 +17,9 @@ struct mcs_spinlock {
    int locked; /* 1 if lock acquired */
    };

    -/*
    - * In order to acquire the lock, the caller should declare a local node and
    - * pass a reference of the node to this function in addition to the lock.
    - * If the lock has already been acquired, then this will proceed to spin
    - * on this node->locked until the previous lock holder sets the node->locked
    - * in mcs_spin_unlock().
    - *
    - * We don't inline mcs_spin_lock() so that perf can correctly account for the
    - * time spent in this lock function.
    - */
    -static noinline
    -void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
    -{
    - struct mcs_spinlock *prev;
    -
    - /* Init node */
    - node->locked = 0;
    - node->next = NULL;
    -
    - prev = xchg(lock, node);
    - if (likely(prev == NULL)) {
    - /* Lock acquired */
    - return;
    - }
    - ACCESS_ONCE(prev->next) = node;
    - smp_wmb();
    - /* Wait until the lock holder passes the lock down */
    - while (!ACCESS_ONCE(node->locked))
    - arch_mutex_cpu_relax();
    -}
    -
    -/*
    - * Releases the lock. The caller should pass in the corresponding node that
    - * was used to acquire the lock.
    - */
    -static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
    -{
    - struct mcs_spinlock *next = ACCESS_ONCE(node->next);
    -
    - if (likely(!next)) {
    - /*
    - * Release the lock by setting it to NULL
    - */
    - if (likely(cmpxchg(lock, node, NULL) == node))
    - return;
    - /* Wait until the next pointer is set */
    - while (!(next = ACCESS_ONCE(node->next)))
    - arch_mutex_cpu_relax();
    - }
    - ACCESS_ONCE(next->locked) = 1;
    - smp_wmb();
    -}
    +extern
    +void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node);
    +extern
    +void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node);

    #endif /* __LINUX_MCS_SPINLOCK_H */
    diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
    index baab8e5..20d9d5c 100644
    --- a/kernel/locking/Makefile
    +++ b/kernel/locking/Makefile
    @@ -13,12 +13,12 @@ obj-$(CONFIG_LOCKDEP) += lockdep.o
    ifeq ($(CONFIG_PROC_FS),y)
    obj-$(CONFIG_LOCKDEP) += lockdep_proc.o
    endif
    -obj-$(CONFIG_SMP) += spinlock.o
    -obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
    +obj-$(CONFIG_SMP) += spinlock.o mcs_spinlock.o
    +obj-$(CONFIG_PROVE_LOCKING) += spinlock.o mcs_spinlock.o
    obj-$(CONFIG_RT_MUTEXES) += rtmutex.o
    obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o
    obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o
    -obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
    +obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o mcs_spinlock.o
    obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o
    obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
    obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o
    diff --git a/include/linux/mcs_spinlock.h b/kernel/locking/mcs_spinlock.c
    similarity index 78%
    copy from include/linux/mcs_spinlock.h
    copy to kernel/locking/mcs_spinlock.c
    index 96f14299..b6f27f8 100644
    --- a/include/linux/mcs_spinlock.h
    +++ b/kernel/locking/mcs_spinlock.c
    @@ -1,7 +1,5 @@
    /*
    - * MCS lock defines
    - *
    - * This file contains the main data structure and API definitions of MCS lock.
    + * MCS lock
    *
    * The MCS lock (proposed by Mellor-Crummey and Scott) is a simple spin-lock
    * with the desirable properties of being fair, and with each cpu trying
    @@ -9,13 +7,20 @@
    * It avoids expensive cache bouncings that common test-and-set spin-lock
    * implementations incur.
    */
    -#ifndef __LINUX_MCS_SPINLOCK_H
    -#define __LINUX_MCS_SPINLOCK_H
    +/*
    + * asm/processor.h may define arch_mutex_cpu_relax().
    + * If it is not defined, cpu_relax() will be used.
    + */
    +#include <asm/barrier.h>
    +#include <asm/cmpxchg.h>
    +#include <asm/processor.h>
    +#include <linux/compiler.h>
    +#include <linux/mcs_spinlock.h>
    +#include <linux/export.h>

    -struct mcs_spinlock {
    - struct mcs_spinlock *next;
    - int locked; /* 1 if lock acquired */
    -};
    +#ifndef arch_mutex_cpu_relax
    +# define arch_mutex_cpu_relax() cpu_relax()
    +#endif

    /*
    * In order to acquire the lock, the caller should declare a local node and
    @@ -23,11 +28,7 @@ struct mcs_spinlock {
    * If the lock has already been acquired, then this will proceed to spin
    * on this node->locked until the previous lock holder sets the node->locked
    * in mcs_spin_unlock().
    - *
    - * We don't inline mcs_spin_lock() so that perf can correctly account for the
    - * time spent in this lock function.
    */
    -static noinline
    void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
    {
    struct mcs_spinlock *prev;
    @@ -47,6 +48,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
    while (!ACCESS_ONCE(node->locked))
    arch_mutex_cpu_relax();
    }
    +EXPORT_SYMBOL_GPL(mcs_spin_lock);

    /*
    * Releases the lock. The caller should pass in the corresponding node that
    @@ -69,5 +71,4 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod
    ACCESS_ONCE(next->locked) = 1;
    smp_wmb();
    }
    -
    -#endif /* __LINUX_MCS_SPINLOCK_H */
    +EXPORT_SYMBOL_GPL(mcs_spin_unlock);
    --
    1.7.4.4




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