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Date: Tue, 10 Dec 2013 09:25:39 -0500
From: Rik van Riel <riel@redhat.com>
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To: Mel Gorman <mgorman@suse.de>
CC: Andrew Morton <akpm@linux-foundation.org>,
        Alex Thorlton <athorlton@sgi.com>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 11/18] mm: fix TLB flush race between migration, and change_protection_range
References: <1386572952-1191-1-git-send-email-mgorman@suse.de> <1386572952-1191-12-git-send-email-mgorman@suse.de>
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On 12/09/2013 02:09 AM, Mel Gorman wrote:

After reading the locking thread that Paul McKenney started,
I wonder if I got the barriers wrong in these functions...

> +#if defined(CONFIG_NUMA_BALANCING) || defined(CONFIG_COMPACTION)
> +/*
> + * Memory barriers to keep this state in sync are graciously provided by
> + * the page table locks, outside of which no page table modifications happen.
> + * The barriers below prevent the compiler from re-ordering the instructions
> + * around the memory barriers that are already present in the code.
> + */
> +static inline bool tlb_flush_pending(struct mm_struct *mm)
> +{
> +	barrier();

Should this be smp_mb__after_unlock_lock(); ?

> +	return mm->tlb_flush_pending;
> +}
> +static inline void set_tlb_flush_pending(struct mm_struct *mm)
> +{
> +	mm->tlb_flush_pending = true;
> +	barrier();
> +}
> +/* Clearing is done after a TLB flush, which also provides a barrier. */
> +static inline void clear_tlb_flush_pending(struct mm_struct *mm)
> +{
> +	barrier();
> +	mm->tlb_flush_pending = false;
> +}

And these smp_mb__before_spinlock() ?

Paul? Peter?

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