linux-kernel - Re: [RFC PATCH] Introduce filesystem type tracking

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Message-ID: <20080520153456.GN2638@parisc-linux.org>
Date:	Tue, 20 May 2008 09:34:57 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Tom Spink <tspink@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] Introduce filesystem type tracking

On Tue, May 20, 2008 at 04:18:14PM +0100, Tom Spink wrote:
> +	
> +	mutex_lock(&type->fs_supers_lock);
> +	if (list_empty(&type->fs_supers) && type->init) {
> +		err = type->init();
> +		if (err) {
> +			mutex_unlock(&type->fs_supers_lock);
> +			spin_unlock(&sb_lock);
> +			destroy_super(s);
> +			return ERR_PTR(err);
> +		}
> +	}
> +	
> +	list_add(&s->s_instances, &type->fs_supers);
> +	mutex_unlock(&type->fs_supers_lock);
> +
>  	s->s_type = type;
>  	strlcpy(s->s_id, type->name, sizeof(s->s_id));
>  	list_add_tail(&s->s_list, &super_blocks);
> -	list_add(&s->s_instances, &type->fs_supers);
> +	
>  	spin_unlock(&sb_lock);

You can't take a mutex while holding a spinlock -- what if you had to
sleep to acquire the mutex?

I imagine you also don't want to hold a spinlock while calling the
->init or ->exit -- what if the fs wants to sleep in there (eg allocate
memory with GFP_KERNEL).

-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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