linux-kernel - Re: [PATCH 1/2] mm: Make follow_pte

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Date:   Tue, 19 Dec 2017 09:05:42 -0800
From:   Joe Perches <joe@...ches.com>
To:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        Josh Triplett <josh@...htriplett.org>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH 1/2] mm: Make follow_pte_pmd an inline

On Tue, 2017-12-19 at 08:58 -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.com>
> 
> The one user of follow_pte_pmd (dax) emits a sparse warning because
> it doesn't know that follow_pte_pmd conditionally returns with the
> pte/pmd locked.  The required annotation is already there; it's just
> in the wrong file.
[]
> diff --git a/include/linux/mm.h b/include/linux/mm.h
[]
> @@ -1324,6 +1324,19 @@ int follow_phys(struct vm_area_struct *vma, unsigned long address,
>  int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
>  			void *buf, int len, int write);
>  
> +static inline int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
> +			     unsigned long *start, unsigned long *end,
> +			     pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
> +{
> +	int res;
> +
> +	/* (void) is needed to make gcc happy */
> +	(void) __cond_lock(*ptlp,
> +			   !(res = __follow_pte_pmd(mm, address, start, end,
> +						    ptepp, pmdpp, ptlp)));

This seems obscure and difficult to read.  Perhaps:

	res = __follow_pte_pmd(mm, address, start, end, ptepp, pmdpp, ptlp);
	(void)__cond_lock(*ptlp, !res);

> +	return res;
> +}