linux-kernel - Re: [PATCH] sysfs: move assignment to be under lock in sysfs_remove

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Message-ID: <8761sflhi1.fsf@tw-ebiederman.twitter.com>
Date:	Tue, 29 Oct 2013 17:39:02 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: move assignment to be under lock in sysfs_remove_dir()

Greg KH <gregkh@...uxfoundation.org> writes:

> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> Linus noticed that the assignment of sd isn't protected by the lock in
> sysfs_remove_dir(), so move the assignment of the variable under the
> lock to be safe.

I don't have a strong feeling either way but how would that matter?
There is only ever one sd associated with a kobj.

And we better be under the sysfs_mutex when the assignment and and
sysfs_remove_dir are called.

> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>
> Tejun, any objection to this patch?  You consolidated the locks back in
> 2007 on this function, and nothing has changed there since then, so odds
> are it's not a problem, but nice to be safe, right?
>
>  fs/sysfs/dir.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index eab59de4..2609f934 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -856,9 +856,10 @@ void sysfs_remove(struct sysfs_dirent *sd)
>   */
>  void sysfs_remove_dir(struct kobject *kobj)
>  {
> -	struct sysfs_dirent *sd = kobj->sd;
> +	struct sysfs_dirent *sd;
>  
>  	spin_lock(&sysfs_assoc_lock);
> +	sd = kobj->sd;
>  	kobj->sd = NULL;
>  	spin_unlock(&sysfs_assoc_lock);
>  
--
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