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

[Robert Hu <robert.hu@vmm.sh.intel.com>]

On Fri, 2016-09-23 at 16:53 +0200, Michal Hocko wrote:
> On Fri 23-09-16 15:56:36, Oleg Nesterov wrote:
> > On 09/23, Robert Ho wrote:
> > >
> > > --- a/fs/proc/task_mmu.c
> > > +++ b/fs/proc/task_mmu.c
> > > @@ -147,7 +147,7 @@ m_next_vma(struct proc_maps_private *priv, struct vm_area_struct *vma)
> > >  static void m_cache_vma(struct seq_file *m, struct vm_area_struct *vma)
> > >  {
> > >  	if (m->count < m->size)	/* vma is copied successfully */
> > > -		m->version = m_next_vma(m->private, vma) ? vma->vm_start : -1UL;
> > > +		m->version = m_next_vma(m->private, vma) ? vma->vm_end : -1UL;
> > >  }
> > 
> > OK.
> > 
> > >  static void *m_start(struct seq_file *m, loff_t *ppos)
> > > @@ -176,14 +176,14 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
> > >  
> > >  	if (last_addr) {
> > >  		vma = find_vma(mm, last_addr);
> > > -		if (vma && (vma = m_next_vma(priv, vma)))
> > > +		if (vma)
> > >  			return vma;
> > >  	}
> > 
> > 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 but at least
> it would provide monotonic results. 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.

Indeed an improvement. I prefer Oleg's approach as well.
> 


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