Messages in this thread | | | Date | Thu, 26 Sep 2013 17:32:08 +0200 | From | Andi Kleen <> | Subject | Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" |
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On Thu, Sep 26, 2013 at 07:52:23AM -0400, Peter Hurley wrote: > On 09/25/2013 11:20 PM, Andi Kleen wrote: > >Lin Ming <minggr@gmail.com> writes: > >> > >>Would you like below patch? > > > >The loop body keeps rather complex state. It could easily > >get confused by parallel RCU changes. > > > >So if the list changes in parallel you may suddenly > >report very bogus values, as the va_start - prev_end > >computation may be bogus. > > > >Perhaps it's ok (may report bogus gaps), but it seems a bit risky. > > I don't understand how the computed gap would be bogus; there > _was_ a list state in which that particular gap existed. The fact
It could change any time as you don't have an atomic view of vm_end / vm_start. It is valid to change the fields with the lock held.
-Andi
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