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

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Date:   Wed, 8 Jan 2020 11:01:41 +0000
From:   Suzuki Kuruppassery Poulose <suzuki.poulose@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     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

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.

Suzuki