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.
--
Michal Hocko
SUSE Labs
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