Re: [PATCH v2 5/5] hwtracing: hisi_ptt: Add dummy callback pmu::read()

[Suzuki K Poulose]

On 19/09/2023 14:03, Yicong Yang wrote:
> On 2023/9/15 20:53, Suzuki K Poulose wrote:
> > On 14/09/2023 12:22, Yicong Yang wrote:
> > > From: Junhao He <hejunhao3@xxxxxxxxxx>
> > >
> > > When start trace with perf option "-C $cpu" and immediately stop it
> > > with SIGTERM or others, the perf core will invoke pmu::read() while
> > > the driver doesn't implement it. Add a dummy pmu::read() to avoid
> > > any issues.
> >
> > What issues are we talking about here ? Shouldn't the core perf
> > skip the call, if pmu::read() is not available ?
>
> Actually no, the core doesn't check it. So I think that's why some PMUs
> like SPE implements a dummy pmu::read() callback. Otherwise we'll
> dereference a NULL pointer.
>
> Currently we only met this on emulated platforms with very slow CPUs,
> follow the instructions in the commit above.

Ok, then it calls for a Fixes tag. Please tag it to the commit that
introduced the PMU.

Suzuki