Re: [RFC PATCH] Introduce filesystem type tracking

[Matthew Wilcox <matthew@wil.cx>]

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).

-- 
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"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
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