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.poulose@xxxxxxx> 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.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..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