linux-kernel - Re: [PATCH 1/6] mm: pagewalk: make error checks more obvious

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Date:   Mon, 22 Aug 2022 13:53:16 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Rolf Eike Beer <eb@...ix.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] mm: pagewalk: make error checks more obvious

On Mon, 22 Aug 2022 15:00:05 +0200 Rolf Eike Beer <eb@...ix.com> wrote:

> The err variable only needs to be checked when it was assigned directly
> before, it is not carried on to any later checks. Move the checks into the
> same "if" conditions where they are assigned. Also just return the error at
> the relevant places. While at it move these err variables to a more local
> scope at some places.
> 
> ...
>
> @@ -593,16 +608,15 @@ int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
>  		walk.mm = vma->vm_mm;
>  
>  		err = walk_page_test(vma->vm_start, vma->vm_end, &walk);
> -		if (err > 0) {
> -			err = 0;
> -			break;
> -		} else if (err < 0)
> -			break;
> +		if (err > 0)
> +			return 0;
> +		else if (err < 0)
> +			return err;
>  
>  		err = __walk_page_range(start_addr, end_addr, &walk);
>  		if (err)
> -			break;
> +			return err;
>  	}
>  
> -	return err;
> +	return 0;
>  }

I'm not really a fan of multiple return points - it tends to lead to
locking/resource leaks as the code evolves.  I don't really think it's
worth redoing the patch for this reason though; the rest looks good.