linux-kernel - Re: mpol_to

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Message-ID: <alpine.DEB.2.00.1210081330160.18768@chino.kir.corp.google.com>
Date:	Mon, 8 Oct 2012 13:35:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	bhutchings@...arflare.com, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: mpol_to_str revisited.

On Mon, 8 Oct 2012, Dave Jones wrote:

> unanswered question: why are the buffer sizes here different ? which is correct?
> 

Given the current set of mempolicy modes and flags, it's 34, but this can 
change if new modes or flags are added with longer names.  I see no reason 
why shmem shouldn't round up to the nearest power-of-2 of 64 like it 
already does, but 50 is certainly safe as well in task_mmu.c.

> diff -durpN '--exclude-from=/home/davej/.exclude' src/git-trees/kernel/linux/fs/proc/task_mmu.c linux-dj/fs/proc/task_mmu.c
> --- src/git-trees/kernel/linux/fs/proc/task_mmu.c	2012-05-31 22:32:46.778150675 -0400
> +++ linux-dj/fs/proc/task_mmu.c	2012-10-04 19:31:41.269988984 -0400
> @@ -1162,6 +1162,7 @@ static int show_numa_map(struct seq_file
>  	struct mm_walk walk = {};
>  	struct mempolicy *pol;
>  	int n;
> +	int ret;
>  	char buffer[50];
>  
>  	if (!mm)
> @@ -1178,7 +1179,11 @@ static int show_numa_map(struct seq_file
>  	walk.mm = mm;
>  
>  	pol = get_vma_policy(proc_priv->task, vma, vma->vm_start);
> -	mpol_to_str(buffer, sizeof(buffer), pol, 0);
> +	memset(buffer, 0, sizeof(buffer));
> +	ret = mpol_to_str(buffer, sizeof(buffer), pol, 0);
> +	if (ret < 0)
> +		return 0;

We should need the mpol_cond_put(pol) here before returning.

> +
>  	mpol_cond_put(pol);
>  
>  	seq_printf(m, "%08lx %s", vma->vm_start, buffer);
> diff -durpN '--exclude-from=/home/davej/.exclude' src/git-trees/kernel/linux/mm/shmem.c linux-dj/mm/shmem.c
> --- src/git-trees/kernel/linux/mm/shmem.c	2012-10-02 15:49:51.977277944 -0400
> +++ linux-dj/mm/shmem.c	2012-10-04 19:32:28.862949907 -0400
> @@ -885,13 +885,15 @@ redirty:
>  static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>  {
>  	char buffer[64];
> +	int ret;
>  
>  	if (!mpol || mpol->mode == MPOL_DEFAULT)
>  		return;		/* show nothing */
>  
> -	mpol_to_str(buffer, sizeof(buffer), mpol, 1);
> -
> -	seq_printf(seq, ",mpol=%s", buffer);
> +	memset(buffer, 0, sizeof(buffer));
> +	ret = mpol_to_str(buffer, sizeof(buffer), mpol, 1);
> +	if (ret > 0)
> +		seq_printf(seq, ",mpol=%s", buffer);
>  }
>  
>  static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
--
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