Messages in this thread | | | Subject | Re: [PATCH v2] mm, proc: Fix region lost in /proc/self/smaps | From | Xiao Guangrong <> | Date | Mon, 19 Sep 2016 15:21:56 +0800 |
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On 09/14/2016 11:38 PM, Oleg Nesterov wrote: > On 09/13, Dave Hansen wrote: >> >> On 09/13/2016 07:59 AM, Oleg Nesterov wrote: >>> I agree. I don't even understand why this was considered as a bug. >>> Obviously, m_stop() which drops mmap_sep should not be called, or >>> all the threads should be stopped, if you want to trust the result. >> >> There was a mapping at a given address. That mapping did not change, it >> was not split, its attributes did not change. But, it didn't show up >> when reading smaps. Folks _actually_ noticed this in a test suite >> looking for that address range in smaps. > > I understand, and I won't argue with any change which makes the things > better. Just I do not think this is a real problem. And this patch can't > fix other oddities and it seems it adds another one (at least) although > I can easily misread this patch and/or the code. > > So we change m_cache_vma(), > > - 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, and another change in m_start() > > - if (vma && (vma = m_next_vma(priv, vma))) > + if (vma) > > means that it can return the same vma if it grows in between. > > show_map_vma() has another change > > + start = max(vma->vm_start, start); > > so it will be reported as _another_ vma, and this doesn't look exactly > right.
We noticed it in the discussion of v1, however it is not bad as Dave said it is about 'address range' rather that vma.
> > And after that *ppos will be falsely incremented... but probably this > doesn't matter because the "if (pos < mm->map_count)" logic in m_start() > looks broken anyway.
The 'broken' can happen only if it is not the first read and m->version is zero (*ppos != 0 && m->version == 0). If i understand the code correctly, only m->buffer overflowed can trigger this, for smaps, each vma only uses ~1k memory that means this could not happen. Right?
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