Re: [PATCH 5/5] perf/arm_dsu: Fix CPU hotplug races

[Robin Murphy]

Hi Suzuki,

On 05/02/2019 11:40, Suzuki K Poulose wrote:
> On 04/02/2019 17:09, Robin Murphy wrote:
> > Like other system PMUs which associate themselves with an arbitrary CPU
> > for housekeeping purposes, arm_dsu has a race between registering the
> > hotplug notifier and registering the PMU device, such that the hotplug
> > niotifier can potentially fire and attempt to migrate the PMU context
> > before the latter is valid. This is easily resolved by inhibiting
> > hotplug until both the notifier and PMU device are successfully set up.
> >
> > For the same reason, also suppress any synchronous notifier calls in the
> > cleanup path if PMU registration fails.
> >
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
>
> Should we add :
>
> Fixes: commit 7520fa99246dade7ab6 ("perf: ARM DynamIQ Shared Unit PMU 
> support")
>
> Either way:
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

Thanks for the reviews! I think this patch is worthwhile for cleanliness 
and consistency, but since it's neither self-contained (with the 
dependency on #4) nor "fix[ing] a real bug that bothers people" I'm not 
convinced it really deserves backporting - unlike the preemption issue, 
actually getting a crash from this race in practice is unlikely enough 
that it would probably require some determined, deliberate effort to 
trigger it with just the right conditions.

Cheers,
Robin.