Re: [PATCH v2] coresight: Serialize enabling/disabling a link device.

[Suzuki K Poulose]

Hi Yabin,

On 12/08/2019 11:38, Suzuki K Poulose wrote:
> Hi Yabin,
>
> On 09/08/2019 22:45, Yabin Cui wrote:
> > When tracing etm data of multiple threads on multiple cpus through perf
> > interface, some link devices are shared between paths of different cpus.
> > It creates race conditions when different cpus wants to enable/disable
> > the same link device at the same time.
> >
> > Example 1:
> > Two cpus want to enable different ports of a coresight funnel, thus
> > calling the funnel enable operation at the same time. But the funnel
> > enable operation isn't reentrantable.
> >
> > Example 2:
> > For an enabled coresight dynamic replicator with refcnt=1, one cpu wants
> > to disable it, while another cpu wants to enable it. Ideally we still have
> > an enabled replicator with refcnt=1 at the end. But in reality the result
> > is uncertain.
> >
> > Since coresight devices claim themselves when enabled for self-hosted
> > usage, the race conditions above usually make the link devices not usable
> > after many cycles.
> >
> > To fix the race conditions, this patch adds a spinlock to serialize
> > enabling/disabling a link device.

Please could you also add :

Fixes : a06ae8609b3dd ("coresight: add CoreSight core layer framework")

Suzuki