linux-kernel - Re: [RFC v3 05/17] RCU free VMAs

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Message-Id: <be153da3-fc43-a70e-ff15-8c57d727f2f3@linux.vnet.ibm.com>
Date:   Wed, 3 May 2017 09:23:31 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com
Subject: Re: [RFC v3 05/17] RCU free VMAs

On 30/04/2017 07:05, Matthew Wilcox wrote:
> 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).

This makes sense.

Thanks,
Laurent