Re: [PATCH 1/4] coresight: tmc-etr: Do not call smp_processor_id() from preemptible

[Robin Murphy]

Hi Suzuki,

On 10/05/2019 10:31, Suzuki K Poulose wrote:
> Instead of using smp_processor_id() to figure out the node,
> use the numa_node_id() for the current CPU node to avoid
> splats like :
>
>   BUG: using smp_processor_id() in preemptible [00000000] code: perf/1743
>   caller is alloc_etr_buf.isra.6+0x80/0xa0
>   CPU: 1 PID: 1743 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
>     alloc_etr_buf.isra.6+0x80/0xa0
>     tmc_alloc_etr_buffer+0x12c/0x1f0
>     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
>
> Fixes: 855ab61c16bf70b646 ("coresight: tmc-etr: Refactor function tmc_etr_setup_perf_buf()")
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 793639f..cae9d8a 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1323,13 +1323,11 @@ static struct etr_perf_buffer *
>   tmc_etr_setup_perf_buf(struct tmc_drvdata *drvdata, struct perf_event *event,
>   		       int nr_pages, void **pages, bool snapshot)
>   {
> -	int node, cpu = event->cpu;
> +	int node;
>   	struct etr_buf *etr_buf;
>   	struct etr_perf_buffer *etr_perf;
>   
> -	if (cpu == -1)
> -		cpu = smp_processor_id();
> -	node = cpu_to_node(cpu);
> +	node = (event->cpu == -1) ? numa_node_id() : cpu_to_node(event->cpu);

If cpu == -1 represents a "don't care" scenario, it might be clearer to 
just use NUMA_NO_NODE instead, and let the allocator handle it.

Robin.

>   
>   	etr_perf = kzalloc_node(sizeof(*etr_perf), GFP_KERNEL, node);
>   	if (!etr_perf)