linux-kernel - Re: [PATCH v3 1/2] mm, proc: Fix region lost in /proc/self/smaps

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Message-ID: <20160923155351.GA1584@redhat.com>
Date:   Fri, 23 Sep 2016 17:53:51 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Robert Ho <robert.hu@...el.com>, pbonzini@...hat.com,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        dave.hansen@...el.com, guangrong.xiao@...ux.intel.com,
        gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stefanha@...hat.com,
        yuhuang@...hat.com, linux-mm@...ck.org,
        ross.zwisler@...ux.intel.com
Subject: Re: [PATCH v3 1/2] mm, proc: Fix region lost in /proc/self/smaps

On 09/23, Michal Hocko wrote:
>
> On Fri 23-09-16 15:56:36, Oleg Nesterov wrote:
> > 
> > I think we can simplify this patch. And imo make it better. How about
> 
> it is certainly less subtle because it doesn't report "sub-vmas".
> 
> > 	if (last_addr) {
> > 		vma = find_vma(mm, last_addr - 1);
> > 		if (vma && vma->vm_start <= last_addr)
> > 			vma = m_next_vma(priv, vma);
> > 		if (vma)
> > 			return vma;
> > 	}
> 
> we would still miss a VMA if the last one got shrunk/split

Not sure I understand what you mean... If the last one was split
we probably should not report the new vma. Nevermind, in any case
yes, sure, this can't "fix" other corner cases.

> So definitely an improvement but
> I guess we really want to document that only full reads provide a
> consistent (at some moment in time) output.

or all the threads were stopped. Agreed. And again, this applies to
any file in /proc.

Oleg.