linux-kernel - Re: [PATCH v2 3/5] userfaultfd: non-cooperative: add event for exit() notification

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Message-Id: <20170201142720.2d3f06ad1ba4410995e5ae0d@linux-foundation.org>
Date:   Wed, 1 Feb 2017 14:27:20 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] userfaultfd: non-cooperative: add event for
 exit() notification

On Wed, 1 Feb 2017 08:35:07 +0200 Mike Rapoport <rppt@...ux.vnet.ibm.com> wrote:

> 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@...ux.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?
>  
> Sure, will add. Do you prefer an incremental patch or update this one?

Either is OK.  I routinely turn replacement patches into deltas so I
and others can see what changed.