linux-kernel - RE: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype list

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Date:	Thu, 23 Jul 2015 14:53:46 +0000
From:	"Elliott, Robert (Server Storage)" <Elliott@...com>
To:	Pan Xinhui <xinhuix.pan@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"bp@...e.de" <bp@...e.de>, "Kani, Toshimitsu" <toshi.kani@...com>,
	"jgross@...e.com" <jgross@...e.com>,
	"mcgrof@...e.com" <mcgrof@...e.com>,
	"mnipxh@....com" <mnipxh@....com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>
Subject: RE: [PATCH] x86/mm/pat: Do a small optimization when dump PAT
 memtype  list

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Pan Xinhui
> Sent: Thursday, July 23, 2015 4:54 AM
> To: linux-kernel@...r.kernel.org
> Subject: [PATCH] x86/mm/pat: Do a small optimization when dump PAT memtype
> list
...
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 268b2c8..6302119 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -1001,45 +1001,42 @@ EXPORT_SYMBOL_GPL(pgprot_writethrough);
> 
>  #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_PAT)
> 
> -static struct memtype *memtype_get_idx(loff_t pos)
> +static struct memtype *memtype_get_idx(struct memtype *entry, loff_t pos)
>  {
> -	struct memtype *print_entry;
>  	int ret;
> 
> -	print_entry  = kzalloc(sizeof(struct memtype), GFP_KERNEL);
> -	if (!print_entry)
> -		return NULL;
> -
>  	spin_lock(&memtype_lock);
> -	ret = rbt_memtype_copy_nth_element(print_entry, pos);
> +	ret = rbt_memtype_copy_nth_element(entry, pos);
>  	spin_unlock(&memtype_lock);
> 
> -	if (!ret) {
> -		return print_entry;
> -	} else {
> -		kfree(print_entry);
> -		return NULL;
> -	}
> +	return ret ? NULL : entry;
>  }
> 
...
>  static void memtype_seq_stop(struct seq_file *seq, void *v)
>  {
> +	kfree(seq->private);
>  }
> 

Consider adding 
	seq->private = NULL; 
so the stale pointer isn't left around.  There's probably not
much risk of accessing it, but NULL is safer in case it is.

---
Robert Elliott, HP Server Storage