Benjamin Herrenschmidt <[email protected]> wrote:
>
> On Mon, 2005-05-23 at 16:28 -0700, Andrew Morton wrote:
>
> > This code can cause deadlocks on CONFIG_SMP && !CONFIG_PREEMPT kernels.
> >
> > Please see http://lkml.org/lkml/2005/3/10/358
> >
> > You (the programmer) *have* to know what context you're running in before
> > doing a voluntary yield. There is simply no way to work this out at
> > runtime.
>
> Hrm... Linus just merged it though...
>
The old version was:
if (!in_softirq())
cond_resched();
Which I guess is OK if the programmer knows that this code is only ever called
a) from softirq context or
b) from process context with no locks/smp_processor_id/etc held.
The new version is:
if (!in_atomic())
cond_resched();
which happens to still be correct as long as a) and b) still hold, which I
assume they do.
Both versions are deadlocky if b) is violated.
So. It sucks before and it sucks after, but we might not be deadlocky.
Problem is, !CONFIG_PREEMPT also disable the beancounting which
might_sleep() depends upon, so it's harder to tell whether all callers are
correct.
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