linux-kernel - Re: [PATCH 4.19 102/115] coresight: tmc-etf: Do not call smp_processor

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Message-ID: <a4c7d0ef-41c5-4c77-6f45-1cc5d153a5c9@arm.com>
Date:   Wed, 8 Jan 2020 11:00:37 +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 4.19 102/115] coresight: tmc-etf: Do not call
 smp_processor_id from preemptible

Hi Greg,

On 07/01/2020 20:55, Greg Kroah-Hartman wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> [ Upstream commit 024c1fd9dbcc1d8a847f1311f999d35783921b7f ]
> 
> 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
>   caller is tmc_alloc_etf_buffer+0x5c/0x60

> Fixes: 2e499bbc1a929ac ("coresight: tmc: implementing TMC-ETF AUX space API")
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Cc: stable <stable@...r.kernel.org> # 4.7+
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Link: https://lore.kernel.org/r/20190620221237.3536-4-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-tmc-etf.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index e31061308e19..4644ac5582cf 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -304,9 +304,7 @@ static void *tmc_alloc_etf_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);

This will break the build on v4.19 to v4.9 as event was not available to
the routine. So please drop this one for now. I will post a backport
separately.

Suzuki