linux-kernel - Re: [PATCH 1/2] lockref: make lockref count signed

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Date:	Wed, 6 Aug 2014 07:44:30 +1000
From:	NeilBrown <neilb@...e.de>
To:	Steven Noonan <steven@...inklabs.net>
Cc:	lkml <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 1/2] lockref: make lockref count signed

On Tue,  5 Aug 2014 12:52:27 -0700 Steven Noonan <steven@...inklabs.net>
wrote:

> There are numerous places where this is casted to a signed value anyway, for
> comparisons checking that the value hasn't been set to the 'dead' value of
> -128. This change turns the count value into a signed integer, which is how
> it's already being treated anyway. This reduces the chance for developer errors
> when making those comparisons.
> 
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: NeilBrown <neilb@...e.de>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Signed-off-by: Steven Noonan <steven@...inklabs.net>

Thanks!  But you missed one "(int)" removal :-)

fs/autofs4/root.c:              if ((int) d_count(active) <= 0)

NeilBrown

> ---
>  fs/dcache.c             | 6 +++---
>  include/linux/lockref.h | 2 +-
>  lib/lockref.c           | 4 ++--
>  3 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 06f6585..f7a592e 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -479,7 +479,7 @@ static void __dentry_kill(struct dentry *dentry)
>  	 * dentry_iput drops the locks, at which point nobody (except
>  	 * transient RCU lookups) can reach this dentry.
>  	 */
> -	BUG_ON((int)dentry->d_lockref.count > 0);
> +	BUG_ON(dentry->d_lockref.count > 0);
>  	this_cpu_dec(nr_dentry);
>  	if (dentry->d_op && dentry->d_op->d_release)
>  		dentry->d_op->d_release(dentry);
> @@ -532,7 +532,7 @@ static inline struct dentry *lock_parent(struct dentry *dentry)
>  	struct dentry *parent = dentry->d_parent;
>  	if (IS_ROOT(dentry))
>  		return NULL;
> -	if (unlikely((int)dentry->d_lockref.count < 0))
> +	if (unlikely(dentry->d_lockref.count < 0))
>  		return NULL;
>  	if (likely(spin_trylock(&parent->d_lock)))
>  		return parent;
> @@ -848,7 +848,7 @@ static void shrink_dentry_list(struct list_head *list)
>  		 * We found an inuse dentry which was not removed from
>  		 * the LRU because of laziness during lookup. Do not free it.
>  		 */
> -		if ((int)dentry->d_lockref.count > 0) {
> +		if (dentry->d_lockref.count > 0) {
>  			spin_unlock(&dentry->d_lock);
>  			if (parent)
>  				spin_unlock(&parent->d_lock);
> diff --git a/include/linux/lockref.h b/include/linux/lockref.h
> index 4bfde0e..8558ff1 100644
> --- a/include/linux/lockref.h
> +++ b/include/linux/lockref.h
> @@ -28,7 +28,7 @@ struct lockref {
>  #endif
>  		struct {
>  			spinlock_t lock;
> -			unsigned int count;
> +			int count;
>  		};
>  	};
>  };
> diff --git a/lib/lockref.c b/lib/lockref.c
> index d2233de..e4c4255 100644
> --- a/lib/lockref.c
> +++ b/lib/lockref.c
> @@ -158,7 +158,7 @@ int lockref_get_not_dead(struct lockref *lockref)
>  
>  	CMPXCHG_LOOP(
>  		new.count++;
> -		if ((int)old.count < 0)
> +		if (old.count < 0)
>  			return 0;
>  	,
>  		return 1;
> @@ -166,7 +166,7 @@ int lockref_get_not_dead(struct lockref *lockref)
>  
>  	spin_lock(&lockref->lock);
>  	retval = 0;
> -	if ((int) lockref->count >= 0) {
> +	if (lockref->count >= 0) {
>  		lockref->count++;
>  		retval = 1;
>  	}


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