On Tue, 2013-09-24 at 16:22 -0700, Jason Low wrote:
> Should we do something similar with __down_read_trylock, such as
> the following?
>
>
> Signed-off-by: Jason Low <jason.low2@xxxxxx>
> ---
> include/asm-generic/rwsem.h | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
> index bb1e2cd..47990dc 100644
> --- a/include/asm-generic/rwsem.h
> +++ b/include/asm-generic/rwsem.h
> @@ -42,6 +42,9 @@ static inline int __down_read_trylock(struct
> rw_semaphore *sem)
> long tmp;
>
> while ((tmp = sem->count) >= 0) {
> + if (sem->count != tmp)
> + continue;
> +
Considering that tmp has just been assigned the value of sem->count, the
added if check failure is unlikely and probably not needed. We should
proceed to cmpxchg below.
> if (tmp == cmpxchg(&sem->count, tmp,
> tmp + RWSEM_ACTIVE_READ_BIAS)) {
> return 1;
Tim
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