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SubjectRe: [PATCH v9 4/5] qrwlock: Use smp_store_release() in write_unlock()
On Tue, Jan 14, 2014 at 11:44:06PM -0500, Waiman Long wrote:
> This patch modifies the queue_write_unlock() function to use the new
> smp_store_release() function (currently in tip). It also removes the
> temporary implementation of smp_load_acquire() and smp_store_release()
> function in qrwlock.c.
>
> This patch will use atomic subtraction instead if the writer field is
> not atomic.
>
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
> include/asm-generic/qrwlock.h | 10 ++++++----
> kernel/locking/qrwlock.c | 34 ----------------------------------
> 2 files changed, 6 insertions(+), 38 deletions(-)
>
> diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
> index 5abb6ca..68f488b 100644
> --- a/include/asm-generic/qrwlock.h
> +++ b/include/asm-generic/qrwlock.h
> @@ -181,11 +181,13 @@ static inline void queue_read_unlock(struct qrwlock *lock)
> static inline void queue_write_unlock(struct qrwlock *lock)
> {
> /*
> - * Make sure that none of the critical section will be leaked out.
> + * If the writer field is atomic, it can be cleared directly.
> + * Otherwise, an atomic subtraction will be used to clear it.
> */
> - smp_mb__before_clear_bit();
> - ACCESS_ONCE(lock->cnts.writer) = 0;
> - smp_mb__after_clear_bit();
> + if (__native_word(lock->cnts.writer))
> + smp_store_release(&lock->cnts.writer, 0);
> + else
> + atomic_sub(_QW_LOCKED, &lock->cnts.rwa);
> }
>
> /*
> diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
> index 053be4d..2727188 100644
> --- a/kernel/locking/qrwlock.c
> +++ b/kernel/locking/qrwlock.c
> @@ -47,40 +47,6 @@
> # define arch_mutex_cpu_relax() cpu_relax()
> #endif
>
> -#ifndef smp_load_acquire
> -# ifdef CONFIG_X86
> -# define smp_load_acquire(p) \
> - ({ \
> - typeof(*p) ___p1 = ACCESS_ONCE(*p); \
> - barrier(); \
> - ___p1; \
> - })
> -# else
> -# define smp_load_acquire(p) \
> - ({ \
> - typeof(*p) ___p1 = ACCESS_ONCE(*p); \
> - smp_mb(); \
> - ___p1; \
> - })
> -# endif
> -#endif
> -
> -#ifndef smp_store_release
> -# ifdef CONFIG_X86
> -# define smp_store_release(p, v) \
> - do { \
> - barrier(); \
> - ACCESS_ONCE(*p) = v; \
> - } while (0)
> -# else
> -# define smp_store_release(p, v) \
> - do { \
> - smp_mb(); \
> - ACCESS_ONCE(*p) = v; \
> - } while (0)
> -# endif
> -#endif
> -
> /*
> * If an xadd (exchange-add) macro isn't available, simulate one with
> * the atomic_add_return() function.
> --
> 1.7.1
>



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