linux-kernel - Re: [PATCH 4.14 65/74] coresight: tmc-etf: Do not call smp_processor

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Date:   Tue, 7 Jan 2020 16:08:25 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.14 65/74] coresight: tmc-etf: Do not call
 smp_processor_id from preemptible

On Tue, Jan 07, 2020 at 09:55:30PM +0100, 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
>  CPU: 2 PID: 2544 Comm: perf Not tainted 5.1.0-rc6-147786-g116841e #344
>  Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Feb  1 2019
>  Call trace:
>   dump_backtrace+0x0/0x150
>   show_stack+0x14/0x20
>   dump_stack+0x9c/0xc4
>   debug_smp_processor_id+0x10c/0x110
>   tmc_alloc_etf_buffer+0x5c/0x60
>   etm_setup_aux+0x1c4/0x230
>   rb_alloc_aux+0x1b8/0x2b8
>   perf_mmap+0x35c/0x478
>   mmap_region+0x34c/0x4f0
>   do_mmap+0x2d8/0x418
>   vm_mmap_pgoff+0xd0/0xf8
>   ksys_mmap_pgoff+0x88/0xf8
>   __arm64_sys_mmap+0x28/0x38
>   el0_svc_handler+0xd8/0x138
>   el0_svc+0x8/0xc
> 
> Use NUMA_NO_NODE hint instead of using the current node for events
> not bound to CPUs.
> 
> 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 336194d059fe..329a201c0c19 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -308,9 +308,7 @@ 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 breaks the build on 4.14 (and I believe 4.19 from the looks of it)
because the event variable is not available without
commit a0f08a6a9fee ("coresight: Communicate perf event to sink buffer
allocation functions") from upstream. I am not sure how this should be
fixed (either backporting the above commit or changing this one somehow)
but it should be dropped in the meantime.

Cheers,
Nathan