linux-kernel - Re: [PATCH 4.19 103/115] coresight: etb10: Do not call smp_processor

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Message-ID: <20200108111719.GA2342287@kroah.com>
Date:   Wed, 8 Jan 2020 12:17:19 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Suzuki Kuruppassery Poulose <suzuki.poulose@....com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 103/115] coresight: etb10: Do not call
 smp_processor_id from preemptible

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@....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@...aro.org>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> > Cc: stable <stable@...r.kernel.org> # 4.6+
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Link: https://lore.kernel.org/r/20190620221237.3536-5-mathieu.poirier@linaro.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Signed-off-by: Sasha Levin <sashal@...nel.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