On Fri, Mar 08, 2013 at 04:07:27PM +0100, Maarten Lankhorst wrote:
> It seems that sysfs has an interesting way of doing the same thing.
> This removes the cpu_relax unfortunately, but if it's really needed,
> it would be better to add this to include/linux/atomic.h to benefit
> all atomic ops users.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankho...@canonical.com>
> ---
Tejun wrote this code originally, so I'll defer to him as to if the
patch below is a valid cleanup or not.
Tejun?
>
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index 2fbdff6..7f968ed 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -165,21 +165,8 @@ struct sysfs_dirent *sysfs_get_active(struct
> sysfs_dirent *sd)
> if (unlikely(!sd))
> return NULL;
>
> - while (1) {
> - int v, t;
> -
> - v = atomic_read(&sd->s_active);
> - if (unlikely(v < 0))
> - return NULL;
> -
> - t = atomic_cmpxchg(&sd->s_active, v, v + 1);
> - if (likely(t == v))
> - break;
> - if (t < 0)
> - return NULL;
> -
> - cpu_relax();
> - }
> + if (!atomic_inc_unless_negative(&sd->s_active))
> + return NULL;
>
> if (likely(!ignore_lockdep(sd)))
> rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
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