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Date: Thu, 2 Feb 2017 15:54:48 +0200
From: Mike Rapoport <rppt@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 3/5] userfaultfd: non-cooperative: add event for
 exit() notification
References: <1485542673-24387-1-git-send-email-rppt@linux.vnet.ibm.com>
 <1485542673-24387-4-git-send-email-rppt@linux.vnet.ibm.com>
 <20170131164132.439f9d30e3a9b3c79bcada3a@linux-foundation.org>
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Hillf Danton <hillf.zj@alibaba-inc.com>, Mike Kravetz <mike.kravetz@oracle.com>, Pavel Emelyanov <xemul@virtuozzo.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>

Hello Andrew,

On Tue, Jan 31, 2017 at 04:41:32PM -0800, Andrew Morton wrote:
> On Fri, 27 Jan 2017 20:44:31 +0200 Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> 
> > Allow userfaultfd monitor track termination of the processes that have
> > memory backed by the uffd.
> > 
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -774,6 +774,30 @@ void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
> >  	}
> >  }
> >  
> > +void userfaultfd_exit(struct mm_struct *mm)
> > +{
> > +	struct vm_area_struct *vma = mm->mmap;
> > +
> > +	while (vma) {
> > +		struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
> > +
> > +		if (ctx && (ctx->features & UFFD_FEATURE_EVENT_EXIT)) {
> > +			struct userfaultfd_wait_queue ewq;
> > +
> > +			userfaultfd_ctx_get(ctx);
> > +
> > +			msg_init(&ewq.msg);
> > +			ewq.msg.event = UFFD_EVENT_EXIT;
> > +
> > +			userfaultfd_event_wait_completion(ctx, &ewq);
> > +
> > +			ctx->features &= ~UFFD_FEATURE_EVENT_EXIT;
> > +		}
> > +
> > +		vma = vma->vm_next;
> > +	}
> > +}
> 
> And we can do the vma walk without locking because the caller (exit_mm)
> knows it now has exclusive access.  Worth a comment?

I've just used your wording, seems to me neat and to the point.