Date: Sat, 29 Apr 2017 22:05:29 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: paulmck@linux.vnet.ibm.com, peterz@infradead.org,
        akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com,
        mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com,
        npiggin@gmail.com, bsingharora@gmail.com
Subject: Re: [RFC v3 05/17] RCU free VMAs
Message-ID: <20170430050529.GH27790@bombadil.infradead.org>
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On Thu, Apr 27, 2017 at 05:52:44PM +0200, Laurent Dufour wrote:
> +static inline bool vma_is_dead(struct vm_area_struct *vma, unsigned int sequence)
> +{
> +	int ret = RB_EMPTY_NODE(&vma->vm_rb);
> +	unsigned seq = ACCESS_ONCE(vma->vm_sequence.sequence);
> +
> +	/*
> +	 * Matches both the wmb in write_seqlock_{begin,end}() and
> +	 * the wmb in vma_rb_erase().
> +	 */
> +	smp_rmb();
> +
> +	return ret || seq != sequence;
> +}

Hang on, this isn't vma_is_dead().  This is vma_has_changed() (possibly
from live to dead, but also possibly grown or shrunk; see your earlier
patch).