linux-kernel - Re: [PATCH 07/13] vfs: lock_two_nondirectories: allow directory args

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Date:	Tue, 11 Feb 2014 16:32:55 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	viro@...IV.linux.org.uk, torvalds@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org, akpm@...ux-foundation.org, dhowells@...hat.com,
	zab@...hat.com, jack@...e.cz, luto@...capital.net, mszeredi@...e.cz
Subject: Re: [PATCH 07/13] vfs: lock_two_nondirectories: allow directory args

On Fri, Feb 07, 2014 at 04:16:44PM -0500, J. Bruce Fields wrote:
> 
> Nit: I find the conditionals here a little complicated.
> 
> Would something like this be clearer? (Untested):
> 
> 	if (inode1 > inode2)
> 		swap(inode1, inode2);
> 
> 	if (inode1 && !S_ISDIR(inode1->i_mode))
> 		mutex_lock(&inode1->i_mutex);
> 
> 	if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
> 		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_NONDIR2);

Yes, much better.  And it becomes nicely symmetric with the unlock function.

Thanks,
Miklos


> 
> --b.
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 4bcdad3..94e41c8 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -944,24 +944,23 @@ EXPORT_SYMBOL(unlock_new_inode);
>  
>  /**
>   * lock_two_nondirectories - take two i_mutexes on non-directory objects
> + *
> + * Lock any non-NULL argument that is not a directory.
> + * Zero, one or two objects may be locked by this function.
> + *
>   * @inode1: first inode to lock
>   * @inode2: second inode to lock
>   */
>  void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
>  {
> -	WARN_ON_ONCE(S_ISDIR(inode1->i_mode));
> -	if (inode1 == inode2 || !inode2) {
> -		mutex_lock(&inode1->i_mutex);
> -		return;
> -	}
> -	WARN_ON_ONCE(S_ISDIR(inode2->i_mode));
> -	if (inode1 < inode2) {
> +	if (inode1 > inode2)
> +		swap(inode1, inode2);
> +
> +	if (inode1 && !S_ISDIR(inode1->i_mode))
>  		mutex_lock(&inode1->i_mutex);
> +
> +	if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
>  		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_NONDIR2);
> -	} else {
> -		mutex_lock(&inode2->i_mutex);
> -		mutex_lock_nested(&inode1->i_mutex, I_MUTEX_NONDIR2);
> -	}
>  }
>  EXPORT_SYMBOL(lock_two_nondirectories);
>  
> @@ -972,8 +971,9 @@ EXPORT_SYMBOL(lock_two_nondirectories);
>   */
>  void unlock_two_nondirectories(struct inode *inode1, struct inode *inode2)
>  {
> -	mutex_unlock(&inode1->i_mutex);
> -	if (inode2 && inode2 != inode1)
> +	if (inode1 && !S_ISDIR(inode1->i_mode))
> +		mutex_unlock(&inode1->i_mutex);
> +	if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
>  		mutex_unlock(&inode2->i_mutex);
>  }
>  EXPORT_SYMBOL(unlock_two_nondirectories);
--
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