Re: [PATCH v1] perf/amlogic: Replace smp_processor_id() with raw_smp_processor_id() in meson_ddr_pmu_create()

[Robin Murphy]

On 17/04/2025 2:20 pm, Will Deacon wrote:
> On Mon, Apr 07, 2025 at 12:02:03PM +0530, Anand Moon wrote:
> > The Amlogic DDR PMU driver meson_ddr_pmu_create() function incorrectly uses
> > smp_processor_id(), which assumes disabled preemption. This leads to kernel
> > warnings during module loading because meson_ddr_pmu_create() can be called
> > in a preemptible context.
> >
> > Following kernel warning and stack trace:
> > [   31.745138] [   T2289] BUG: using smp_processor_id() in preemptible [00000000] code: (udev-worker)/2289
> > [   31.745154] [   T2289] caller is debug_smp_processor_id+0x28/0x38
> > [   31.745172] [   T2289] CPU: 4 UID: 0 PID: 2289 Comm: (udev-worker) Tainted: GW 6.14.0-0-MANJARO-ARM #1 59519addcbca6ba8de735e151fd7b9e97aac7ff0
> > [   31.745181] [   T2289] Tainted: [W]=WARN
> > [   31.745183] [   T2289] Hardware name: Hardkernel ODROID-N2Plus (DT)
> > [   31.745188] [   T2289] Call trace:
> > [   31.745191] [   T2289]  show_stack+0x28/0x40 (C)
> > [   31.745199] [   T2289]  dump_stack_lvl+0x4c/0x198
> > [   31.745205] [   T2289]  dump_stack+0x20/0x50
> > [   31.745209] [   T2289]  check_preemption_disabled+0xec/0xf0
> > [   31.745213] [   T2289]  debug_smp_processor_id+0x28/0x38
> > [   31.745216] [   T2289]  meson_ddr_pmu_create+0x200/0x560 [meson_ddr_pmu_g12 8095101c49676ad138d9961e3eddaee10acca7bd]
> > [   31.745237] [   T2289]  g12_ddr_pmu_probe+0x20/0x38 [meson_ddr_pmu_g12 8095101c49676ad138d9961e3eddaee10acca7bd]
> > [   31.745246] [   T2289]  platform_probe+0x98/0xe0
> > [   31.745254] [   T2289]  really_probe+0x144/0x3f8
> > [   31.745258] [   T2289]  __driver_probe_device+0xb8/0x180
> > [   31.745261] [   T2289]  driver_probe_device+0x54/0x268
> > [   31.745264] [   T2289]  __driver_attach+0x11c/0x288
> > [   31.745267] [   T2289]  bus_for_each_dev+0xfc/0x160
> > [   31.745274] [   T2289]  driver_attach+0x34/0x50
> > [   31.745277] [   T2289]  bus_add_driver+0x160/0x2b0
> > [   31.745281] [   T2289]  driver_register+0x78/0x120
> > [   31.745285] [   T2289]  __platform_driver_register+0x30/0x48
> > [   31.745288] [   T2289]  init_module+0x30/0xfe0 [meson_ddr_pmu_g12 8095101c49676ad138d9961e3eddaee10acca7bd]
> > [   31.745298] [   T2289]  do_one_initcall+0x11c/0x438
> > [   31.745303] [   T2289]  do_init_module+0x68/0x228
> > [   31.745311] [   T2289]  load_module+0x118c/0x13a8
> > [   31.745315] [   T2289]  __arm64_sys_finit_module+0x274/0x390
> > [   31.745320] [   T2289]  invoke_syscall+0x74/0x108
> > [   31.745326] [   T2289]  el0_svc_common+0x90/0xf8
> > [   31.745330] [   T2289]  do_el0_svc+0x2c/0x48
> > [   31.745333] [   T2289]  el0_svc+0x60/0x150
> > [   31.745337] [   T2289]  el0t_64_sync_handler+0x80/0x118
> > [   31.745341] [   T2289]  el0t_64_sync+0x1b8/0x1c0
> >
> > Changes replaces smp_processor_id() with raw_smp_processor_id() to
> > ensure safe CPU ID retrieval in preemptible contexts.
> >
> > Cc: Jiucheng Xu <jiucheng.xu@xxxxxxxxxxx>
> > Fixes: 2016e2113d35 ("perf/amlogic: Add support for Amlogic meson G12 SoC DDR PMU driver")
> > Signed-off-by: Anand Moon <linux.amoon@xxxxxxxxx>
> > ---
> >   drivers/perf/amlogic/meson_ddr_pmu_core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/perf/amlogic/meson_ddr_pmu_core.c b/drivers/perf/amlogic/meson_ddr_pmu_core.c
> > index 07446d784a1a..c1e755c356a3 100644
> > --- a/drivers/perf/amlogic/meson_ddr_pmu_core.c
> > +++ b/drivers/perf/amlogic/meson_ddr_pmu_core.c
> > @@ -511,7 +511,7 @@ int meson_ddr_pmu_create(struct platform_device *pdev)
> >   
> >   	fmt_attr_fill(pmu->info.hw_info->fmt_attr);
> >   
> > -	pmu->cpu = smp_processor_id();
> > +	pmu->cpu = raw_smp_processor_id();
> >   
> >   	name = devm_kasprintf(&pdev->dev, GFP_KERNEL, DDR_PERF_DEV_NAME);
> >   	if (!name)
>
>
> Bah, this follows what the other drivers are doing but I continue to
> dislike the races we have between CPU hotplug and perf PMU registration.
>
> Robin -- did you have a crack at fixing that or did I dream it?

I've had "Perf core should do cpu hotplug!" written on the whiteboard 
behind my desk for about 5 years now, does that count? :)

However my initial plan was to at least factor out some of this common 
boilerplate within drivers/perf itself - I currently have one WIP patch 
from last year making a start on that, but I reckon I can find a way to 
make it crucial for the other PMU driver work I've already got scheduled 
this quarter (assuming I win the game of whack-a-mole against IOMMU race 
conditions soon enough...)

Cheers,
Robin.