Neeraj Upadhyay d88c1e77fd ANDROID: irq: manage: Export irq_do_set_affinity symbol ...

Vendor kernel modules may implement irq balancers, which could
take irq desc lock of an irq and then based on current affinity
mask or affinity hint, reconfigure the affinity of that irq.
For example : For an irq, for which affinity is broken i.e. all
the cpus in its affinity mask have gone offline. For such irqs,
we might want to reset the affinity, when the original set of
affined cpus, come back online. desc->affinity_hint can be used
for figuring out the original affinity. So, the sequence for doing
this becomes:

desc = irq_to_desc(i);
raw_spin_lock(&desc->lock);
affinity = desc->affinity_hint;
raw_spin_unlock(&desc->lock);
irq_set_affinity_hint(i, affinity);

Here, we need to release the desc lock before calling the exported
api irq_set_affinity_hint(). This creates a window where, after
unlocking desc lock and before calling irq_set_affinity_hint(),
where this setting can race with other irq_set_affinity_hint()
callers. So, export irq_do_set_affinity() symbol to provide an
api, which can be called with desc lock held.

Bug: 187157600
Change-Id: Ifad88bfaa1e7eec09c3fe5a9dd7d1d421362b41e
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>

2021-05-06 14:58:19 +00:00

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