Quoting Tvrtko Ursulin (2018-02-19 09:25:00)
> On 16/02/2018 10:13, Chris Wilson wrote:
> > Afaict, it's complaining that because the writer is special the reader
> > needs irq protection. Which I don't understand, as the point is that the
> > writer can run concurrently to the readers (the readers have to
> > restart). What am I missing?
> As discussed on IRC, issue is courtesy of perf read callback running in
> hardirq context, that the reader can interrupt the writer and so
> incorrectly declare a stable sequence number while reading the mixed up
> version of the underlying data.
> modify some fields
> <Reader IRQ...
> read seqno
> read fields
> re-read seqno -> OK
> >..Reader IRQ
> modify other fields
> So we need to go back to the first, irqsave version. Do you want to
> pursue this change right now or leave it for some future work?
It's a small optimisation (hopefully ;) so pursue at leisure or in the
context of wider work.
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