linux-kernel - Re: [PATCH] mm: numa: Guarantee that tlb_flush_pending updates are visible before page table updates

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Date:	Wed, 11 Dec 2013 06:44:47 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alex Thorlton <athorlton@....com>,
	Rik van Riel <riel@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: numa: Guarantee that tlb_flush_pending updates are
 visible before page table updates

On Wed, Dec 11, 2013 at 01:21:09PM +0000, Mel Gorman wrote:
> According to documentation on barriers, stores issued before a LOCK can
> complete after the lock implying that it's possible tlb_flush_pending can
> be visible after a page table update. As per revised documentation, this patch
> adds a smp_mb__before_spinlock to guarantee the correct ordering.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Assuming that there is a lock acquisition after calls to
set_tlb_flush_pending():

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

(I don't see set_tlb_flush_pending() in mainline.)

> ---
>  include/linux/mm_types.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index c122bb1..a12f2ab 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -482,7 +482,12 @@ static inline bool tlb_flush_pending(struct mm_struct *mm)
>  static inline void set_tlb_flush_pending(struct mm_struct *mm)
>  {
>  	mm->tlb_flush_pending = true;
> -	barrier();
> +
> +	/*
> +	 * Guarantee that the tlb_flush_pending store does not leak into the
> +	 * critical section updating the page tables
> +	 */
> +	smp_mb__before_spinlock();
>  }
>  /* Clearing is done after a TLB flush, which also provides a barrier. */
>  static inline void clear_tlb_flush_pending(struct mm_struct *mm)
> 

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