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

[Suzuki Kuruppassery Poulose]

Greg,

On 07/01/2020 20:55, Greg Kroah-Hartman wrote:
> From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>
> [ 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@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.6+
> Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20190620221237.3536-5-mathieu.poirier@xxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>   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.

Suzuki