Re: [PATCH 4.19 103/115] coresight: etb10: Do not call smp_processor_id from preemptible

Greg Kroah-Hartman
2020-01-08T11:17:54Z

On Wed, Jan 08, 2020 at 11:01:41AM +0000, Suzuki Kuruppassery Poulose wrote:
> Greg,
>
> On 07/01/2020 20:55, Greg Kroah-Hartman wrote:
> > From: Suzuki K Poulose <suzuki.poulose@arm.com>
> >
> > [ Upstream commit 730766bae3280a25d40ea76a53dc6342e84e6513 ]
> >
> > During a perf session we try to allocate buffers on the "node" associated
> > with the CPU the event is bound to. If it is not bound to a CPU, we
> > use the current CPU node, using smp_processor_id(). However this is unsafe
> > in a pre-emptible context and could generate the splats as below :
> >
>
> > BUG: using smp_processor_id() in preemptible [00000000] code: perf/2544
> >
> > Use NUMA_NO_NODE hint instead of using the current node for events
> > not bound to CPUs.
> >
> > Fixes: 2997aa4063d97fdb39 ("coresight: etb10: implementing AUX API")
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Cc: stable <stable@vger.kernel.org> # 4.6+
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Link: https://lore.kernel.org/r/20190620221237.3536-5-mathieu.poirier@linaro.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> > drivers/hwtracing/coresight/coresight-etb10.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
> > index 0dad8626bcfb..0a59bf3af40b 100644
> > --- a/drivers/hwtracing/coresight/coresight-etb10.c
> > +++ b/drivers/hwtracing/coresight/coresight-etb10.c
> > @@ -275,9 +275,7 @@ static void *etb_alloc_buffer(struct coresight_device *csdev, int cpu,
> > int node;
> > struct cs_buffers *buf;
> > - if (cpu == -1)
> > - cpu = smp_processor_id();
> > - node = cpu_to_node(cpu);
> > + node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
>
> Please drop this patch too, from the list as it will break the build
> with undefined "event" variable. I will post a backport soon.

Also now dropped, thanks.

greg k-h