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SubjectRe: tun.c patch to fix "smp_processor_id() in preemptible code"
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On Tue, 2004-10-19 at 18:33, David S. Miller wrote:
> On Tue, 19 Oct 2004 18:10:58 -0400
> Lee Revell <rlrevell@joe-job.com> wrote:
>
> > /*
> > * Since receiving is always initiated from a tasklet (in iucv.c),
> > * we must use netif_rx_ni() instead of netif_rx()
> > */
> >
> > This implies that the author thought it was a matter of correctness to
> > use netif_rx_ni vs. netif_rx. But it looks like the only difference is
> > that the former sacrifices preempt-safety for performance.
>
> You can't really delete netif_rx_ni(), so if there is a preemptability
> issue, just add the necessary preemption protection around the softirq
> checks.
>

Why not? AIUI the only valid reason to use preempt_disable/enable is in
the case of per-CPU data. This is not "real" per-CPU data, it's a
performance hack. Therefore it would be incorrect to add the preemption
protection, the fix is not to manually call do_softirq but to let the
softirq run by the normal mechanism.

Am I missing something?

Lee

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