linux-kernel - Re: [PATCH] kref: remove kref

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Date:	Tue, 16 Mar 2010 08:31:03 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	NeilBrown <neilb@...e.de>
Cc:	Greg KH <gregkh@...e.de>, Mimi Zohar <zohar@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kref: remove kref_set

Quoting NeilBrown (neilb@...e.de):
> 
> 
> Of the three uses of kref_set in the kernel:
> 
>  One really should be kref_put as the code is letting go of a
>     reference,
>  Two really should be kref_init because the kref is being
>     initialised.
> 
> This suggests that making kref_set available encourages bad code.
> So fix the three uses and remove kref_set completely.
> 
> Signed-off-by: NeilBrown <neilb@...e.de>

No objection to the user_namespace.c hunk - haven't tested it
but it certainly had better work with what you have.

Acked-by: Serge Hallyn <serue@...ibm.com>

thanks,
-serge

> --
> 
> The two 'kref_init' calls in ima_iint.c could equally be a single
> call after the kmem_cache_alloc in ima_inode_alloc, but this version
> was the minimal code change.
> 
> 
> diff --git a/include/linux/kref.h b/include/linux/kref.h
> index b0cb0eb..13003ee 100644
> --- a/include/linux/kref.h
> +++ b/include/linux/kref.h
> @@ -21,7 +21,6 @@ struct kref {
>  	atomic_t refcount;
>  };
> 
> -void kref_set(struct kref *kref, int num);
>  void kref_init(struct kref *kref);
>  void kref_get(struct kref *kref);
>  int kref_put(struct kref *kref, void (*release) (struct kref *kref));
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 076c7c8..b2d70d3 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -54,8 +54,8 @@ int create_user_ns(struct cred *new)
>  #endif
>  	/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
> 
> -	/* alloc_uid() incremented the userns refcount.  Just set it to 1 */
> -	kref_set(&ns->kref, 1);
> +	/* root_user holds a reference to ns, our reference can be dropped */
> +	put_user_ns(ns);
> 
>  	return 0;
>  }
> diff --git a/lib/kref.c b/lib/kref.c
> index 9ecd6e8..69761d3 100644
> --- a/lib/kref.c
> +++ b/lib/kref.c
> @@ -15,23 +15,13 @@
>  #include <linux/module.h>
> 
>  /**
> - * kref_set - initialize object and set refcount to requested number.
> - * @kref: object in question.
> - * @num: initial reference counter
> - */
> -void kref_set(struct kref *kref, int num)
> -{
> -	atomic_set(&kref->refcount, num);
> -	smp_mb();
> -}
> -
> -/**
>   * kref_init - initialize object.
>   * @kref: object in question.
>   */
>  void kref_init(struct kref *kref)
>  {
> -	kref_set(kref, 1);
> +	atomic_set(&kref->refcount, 1);
> +	smp_mb();
>  }
> 
>  /**
> @@ -71,7 +61,6 @@ int kref_put(struct kref *kref, void (*release)(struct kref *kref))
>  	return 0;
>  }
> 
> -EXPORT_SYMBOL(kref_set);
>  EXPORT_SYMBOL(kref_init);
>  EXPORT_SYMBOL(kref_get);
>  EXPORT_SYMBOL(kref_put);
> diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
> index 2d4d05d..91c31d8 100644
> --- a/security/integrity/ima/ima_iint.c
> +++ b/security/integrity/ima/ima_iint.c
> @@ -93,7 +93,7 @@ void iint_free(struct kref *kref)
>  		       iint->opencount);
>  		iint->opencount = 0;
>  	}
> -	kref_set(&iint->refcount, 1);
> +	kref_init(&iint->refcount);
>  	kmem_cache_free(iint_cache, iint);
>  }
> 
> @@ -132,7 +132,7 @@ static void init_once(void *foo)
>  	iint->readcount = 0;
>  	iint->writecount = 0;
>  	iint->opencount = 0;
> -	kref_set(&iint->refcount, 1);
> +	kref_init(&iint->refcount);
>  }
> 
>  static int __init ima_iintcache_init(void)
--
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