On Thu, Oct 22, 2020 at 06:19:37PM +0530, Sai Prakash Ranjan wrote:
> On 2020-10-22 17:02, Peter Zijlstra wrote:
> > On Thu, Oct 22, 2020 at 04:27:52PM +0530, Sai Prakash Ranjan wrote:
> >
> > > Looking at the ETR and other places in the kernel, ETF and the
> > > ETB are the only places trying to dereference the task(owner)
> > > in tmc_enable_etf_sink_perf() which is also called from the
> > > sched_in path as in the call trace.
> >
> > > @@ -391,6 +392,10 @@ static void *tmc_alloc_etf_buffer(struct
> > > coresight_device *csdev,
> > > {
> > > int node;
> > > struct cs_buffers *buf;
> > > + struct task_struct *task = READ_ONCE(event->owner);
> > > +
> > > + if (!task || is_kernel_event(event))
> > > + return NULL;
> >
> >
> > This is *wrong*... why do you care about who owns the events?
> >
>
> The original issue was the owner being NULL and causing
> a NULL pointer dereference. I did ask some time back
> if it is valid for the owner to be NULL [1] and should
> probably be handled in events core?
No, what I asked is why do you care about ->owner to begin with? That
seems wrong. A driver should not touch ->owner _at_all_.
