linux-kernel - Re: [PATCH 02/11] kernfs: use idr instead of ida to manage inode number

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Message-ID: <20170612181447.GG19206@htj.duckdns.org>
Date:   Mon, 12 Jun 2017 14:14:47 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Shaohua Li <shli@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        gregkh@...uxfoundation.org, hch@....de, axboe@...com,
        rostedt@...dmis.org, lizefan@...wei.com, Kernel-team@...com,
        Shaohua Li <shli@...com>
Subject: Re: [PATCH 02/11] kernfs: use idr instead of ida to manage inode
 number

Hello,

On Fri, Jun 02, 2017 at 02:53:55PM -0700, Shaohua Li wrote:
> @@ -630,7 +633,11 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
>  	if (!kn)
>  		goto err_out1;
>  
> -	ret = ida_simple_get(&root->ino_ida, 1, 0, GFP_KERNEL);
> +	idr_preload(GFP_KERNEL);
> +	spin_lock(&kernfs_idr_lock);
> +	ret = idr_alloc(&root->ino_idr, kn, 1, 0, GFP_ATOMIC);
> +	spin_unlock(&kernfs_idr_lock);
> +	idr_preload_end();

So, this ends up populating the idr w/ a kn which isn't fully
initialized yet, which can lead to bugs which are difficult to hunt
down as we're gonna allow kn's to be looked up through ino / gen.  We
probably should allocate with NULL here and populate the actual
pointer with idr_replace() after the kn is fully initialized / online.

Thanks.

-- 
tejun