Re: [PATCH 1/2] coresight: Do not call smp_processor_id() from preemptible

[Suzuki K Poulose]

On 08/05/2019 17:39, Mathieu Poirier wrote:

Hi Suzuki,

On Fri, 3 May 2019 at 10:04, Suzuki K Poulose <suzuki.poul...@arm.com> 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

That is very interesting...

Fixes: 855ab61c16bf70b646 ("coresight: tmc-etr: Refactor function 
tmc_etr_setup_perf_buf()")
Cc: Mathieu Poirier <mathieu.poir...@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---
  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..74578bd 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);

Seems to me using numa_node_id() simply circumvent function
debug_smp_processor_id() and using get_cpu() and put_cpu() would be
more appropriate.  But I'll trust the NUMA people have thought about
this long before me.  Would you mind sending another revision that fix
the same code for ETB and ETF?

Sure, will send it soon.

Suzuki