[PATCH] sysfs: use atomic_inc_unless_negative in sysfs_get_active

[PATCH] sysfs: use atomic_inc_unless_negative in sysfs_get_active

[Maarten Lankhorst]

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.lankhorst@canonical.com>
 ---

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_);

Re: [PATCH] sysfs: use atomic_inc_unless_negative in sysfs_get_active

[Greg KH]

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.lankhorst@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_);

Re: [PATCH] sysfs: use atomic_inc_unless_negative in sysfs_get_active

[Tejun Heo]

On Mon, Mar 18, 2013 at 05:14:18PM -0700, Greg KH wrote:
> 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.lankhorst@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.

Yeah, I think that code predates atomic_inc_unless_negative().

> > 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;

Looks good to me.

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun