linux-kernel - Re: [PATCH 2/7] uprobes: Fold xol_alloc_area() into get_xol

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Date:	Wed, 9 Jan 2013 11:16:54 +0100
From:	Anton Arapov <anton@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Frank Eigler <fche@...hat.com>,
	Josh Stone <jistone@...hat.com>,
	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] uprobes: Fold xol_alloc_area() into get_xol_area()

On Mon, Dec 31, 2012 at 06:52:16PM +0100, Oleg Nesterov wrote:
> Currently only xol_get_insn_slot() does get_xol_area() + xol_alloc_area(),
> but this will have more users and we do not want to copy-and-paste this
> code. This patch simply moves xol_alloc_area() into get_xol_area() to
> simplify the current and future code.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/events/uprobes.c |   38 ++++++++++++++++----------------------
>  1 files changed, 16 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 1456f7d..ef81162 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1070,27 +1070,21 @@ static int xol_add_vma(struct xol_area *area)
>  	return ret;
>  }
>  
> -static struct xol_area *get_xol_area(struct mm_struct *mm)
> -{
> -	struct xol_area *area;
> -
> -	area = mm->uprobes_state.xol_area;
> -	smp_read_barrier_depends();	/* pairs with wmb in xol_add_vma() */
> -
> -	return area;
> -}
> -
>  /*
> - * xol_alloc_area - Allocate process's xol_area.
> - * This area will be used for storing instructions for execution out of
> - * line.
> + * get_alloc_area - Allocate process's xol_area if necessary.
> + * This area will be used for storing instructions for execution out of line.
>   *
>   * Returns the allocated area or NULL.
>   */

+ * get_xol_area ....

Anton.

> -static struct xol_area *xol_alloc_area(void)
> +static struct xol_area *get_xol_area(void)
>  {
> +	struct mm_struct *mm = current->mm;
>  	struct xol_area *area;
>  
> +	area = mm->uprobes_state.xol_area;
> +	if (area)
> +		goto ret;
> +
>  	area = kzalloc(sizeof(*area), GFP_KERNEL);
>  	if (unlikely(!area))
>  		goto out;
> @@ -1113,7 +1107,10 @@ static struct xol_area *xol_alloc_area(void)
>   free_area:
>  	kfree(area);
>   out:
> -	return get_xol_area(current->mm);
> +	area = mm->uprobes_state.xol_area;
> + ret:
> +	smp_read_barrier_depends();     /* pairs with wmb in xol_add_vma() */
> +	return area;
>  }
>  
>  /*
> @@ -1189,14 +1186,11 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
>  	unsigned long offset;
>  	void *vaddr;
>  
> -	area = get_xol_area(current->mm);
> -	if (!area) {
> -		area = xol_alloc_area();
> -		if (!area)
> -			return 0;
> -	}
> -	current->utask->xol_vaddr = xol_take_insn_slot(area);
> +	area = get_xol_area();
> +	if (!area)
> +		return 0;
>  
> +	current->utask->xol_vaddr = xol_take_insn_slot(area);
>  	/*
>  	 * Initialize the slot if xol_vaddr points to valid
>  	 * instruction slot.
> -- 
> 1.5.5.1
> 
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