[PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Alexandre Ghiti]

As reported in [1], the use of smp_processor_id() in
pmu_sbi_device_probe() must be protected by disabling the preemption, so
simple use get_cpu()/put_cpu() instead.

Reported-by: Nam Cao <namcao@linutronix.de>
Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 31a17a56eb3b..25b1b699b3e2 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -1373,11 +1373,15 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 
 	/* SBI PMU Snapsphot is only available in SBI v2.0 */
 	if (sbi_v2_available) {
+		int cpu;
+
 		ret = pmu_sbi_snapshot_alloc(pmu);
 		if (ret)
 			goto out_unregister;
 
-		ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
+		cpu = get_cpu();
+
+		ret = pmu_sbi_snapshot_setup(pmu, cpu);
 		if (ret) {
 			/* Snapshot is an optional feature. Continue if not available */
 			pmu_sbi_snapshot_free(pmu);
@@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
 			 */
 			static_branch_enable(&sbi_pmu_snapshot_available);
 		}
+		put_cpu();
 	}
 
 	register_sysctl("kernel", sbi_pmu_sysctl_table);
-- 
2.39.2

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Anup Patel]

On Mon, Aug 26, 2024 at 10:22 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simple use get_cpu()/put_cpu() instead.
>
> Reported-by: Nam Cao <namcao@linutronix.de>
> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

LGTM.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 31a17a56eb3b..25b1b699b3e2 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -1373,11 +1373,15 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>
>         /* SBI PMU Snapsphot is only available in SBI v2.0 */
>         if (sbi_v2_available) {
> +               int cpu;
> +
>                 ret = pmu_sbi_snapshot_alloc(pmu);
>                 if (ret)
>                         goto out_unregister;
>
> -               ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
> +               cpu = get_cpu();
> +
> +               ret = pmu_sbi_snapshot_setup(pmu, cpu);
>                 if (ret) {
>                         /* Snapshot is an optional feature. Continue if not available */
>                         pmu_sbi_snapshot_free(pmu);
> @@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>                          */
>                         static_branch_enable(&sbi_pmu_snapshot_available);
>                 }
> +               put_cpu();
>         }
>
>         register_sysctl("kernel", sbi_pmu_sysctl_table);
> --
> 2.39.2
>

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Nam Cao]

On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simple use get_cpu()/put_cpu() instead.
> 
> Reported-by: Nam Cao <namcao@linutronix.de>
> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Tested-by: Nam Cao <namcao@linutronix.de>

I think this also needs:
Fixes: a8625217a054 ("drivers/perf: riscv: Implement SBI PMU snapshot function")

Best regards,
Nam

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Alexandre Ghiti]

On 26/08/2024 19:31, Nam Cao wrote:
> On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
>> As reported in [1], the use of smp_processor_id() in
>> pmu_sbi_device_probe() must be protected by disabling the preemption, so
>> simple use get_cpu()/put_cpu() instead.
>>
>> Reported-by: Nam Cao <namcao@linutronix.de>
>> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
>> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> Tested-by: Nam Cao <namcao@linutronix.de>
>
> I think this also needs:
> Fixes: a8625217a054 ("drivers/perf: riscv: Implement SBI PMU snapshot function")


Indeed, thanks for the tag!


>
> Best regards,
> Nam
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Andrea Parri]

On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simple use get_cpu()/put_cpu() instead.

  simply


> Reported-by: Nam Cao <namcao@linutronix.de>

Reported-by: Andrea Parri <parri.andrea@gmail.com>


> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Tested-by: Andrea Parri <parri.andrea@gmail.com>

  Andrea

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Alexandre Ghiti]

Hi Andrea,

On Mon, Aug 26, 2024 at 9:36 PM Andrea Parri <parri.andrea@gmail.com> wrote:
>
> On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
> > As reported in [1], the use of smp_processor_id() in
> > pmu_sbi_device_probe() must be protected by disabling the preemption, so
> > simple use get_cpu()/put_cpu() instead.
>
>   simply
>
>
> > Reported-by: Nam Cao <namcao@linutronix.de>
>
> Reported-by: Andrea Parri <parri.andrea@gmail.com>

I added it at first but since there is no link to a bug report,
checkpatch complains so I removed it. But I have just checked the
documentation which states:

"The tag should be followed by a Closes: tag pointing to the report,
unless the report is not available on the web"

So I'm sorry about that, it won't happen again.

Thanks,

Alex


>
>
> > Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
>
> Tested-by: Andrea Parri <parri.andrea@gmail.com>
>
>   Andrea

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Will Deacon]

On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
> As reported in [1], the use of smp_processor_id() in
> pmu_sbi_device_probe() must be protected by disabling the preemption, so
> simple use get_cpu()/put_cpu() instead.
> 
> Reported-by: Nam Cao <namcao@linutronix.de>
> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 31a17a56eb3b..25b1b699b3e2 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -1373,11 +1373,15 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>  
>  	/* SBI PMU Snapsphot is only available in SBI v2.0 */
>  	if (sbi_v2_available) {
> +		int cpu;
> +
>  		ret = pmu_sbi_snapshot_alloc(pmu);
>  		if (ret)
>  			goto out_unregister;
>  
> -		ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
> +		cpu = get_cpu();
> +
> +		ret = pmu_sbi_snapshot_setup(pmu, cpu);
>  		if (ret) {
>  			/* Snapshot is an optional feature. Continue if not available */
>  			pmu_sbi_snapshot_free(pmu);
> @@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>  			 */
>  			static_branch_enable(&sbi_pmu_snapshot_available);
>  		}
> +		put_cpu();

Are you sure it's safe to enable the static key with preemption disabled?
I thought that could block on a mutex.

Will

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Alexandre Ghiti]

Hi Will,

On Tue, Aug 27, 2024 at 2:53 PM Will Deacon <will@kernel.org> wrote:
>
> On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
> > As reported in [1], the use of smp_processor_id() in
> > pmu_sbi_device_probe() must be protected by disabling the preemption, so
> > simple use get_cpu()/put_cpu() instead.
> >
> > Reported-by: Nam Cao <namcao@linutronix.de>
> > Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
> > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> > ---
> >  drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> > index 31a17a56eb3b..25b1b699b3e2 100644
> > --- a/drivers/perf/riscv_pmu_sbi.c
> > +++ b/drivers/perf/riscv_pmu_sbi.c
> > @@ -1373,11 +1373,15 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
> >
> >       /* SBI PMU Snapsphot is only available in SBI v2.0 */
> >       if (sbi_v2_available) {
> > +             int cpu;
> > +
> >               ret = pmu_sbi_snapshot_alloc(pmu);
> >               if (ret)
> >                       goto out_unregister;
> >
> > -             ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
> > +             cpu = get_cpu();
> > +
> > +             ret = pmu_sbi_snapshot_setup(pmu, cpu);
> >               if (ret) {
> >                       /* Snapshot is an optional feature. Continue if not available */
> >                       pmu_sbi_snapshot_free(pmu);
> > @@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
> >                        */
> >                       static_branch_enable(&sbi_pmu_snapshot_available);
> >               }
> > +             put_cpu();
>
> Are you sure it's safe to enable the static key with preemption disabled?
> I thought that could block on a mutex.

Yep, it seems you're right, thanks for jumping in.

I'm discussing with Atish how to fix that differently, I'll be back
with another version very soon.

Thanks again,

Alex

>
> Will

Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code

[Atish Patra]

On 8/28/24 5:36 AM, Alexandre Ghiti wrote:
> Hi Will,
> 
> On Tue, Aug 27, 2024 at 2:53 PM Will Deacon <will@kernel.org> wrote:
>>
>> On Mon, Aug 26, 2024 at 06:52:10PM +0200, Alexandre Ghiti wrote:
>>> As reported in [1], the use of smp_processor_id() in
>>> pmu_sbi_device_probe() must be protected by disabling the preemption, so
>>> simple use get_cpu()/put_cpu() instead.
>>>
>>> Reported-by: Nam Cao <namcao@linutronix.de>
>>> Closes: https://lore.kernel.org/linux-riscv/20240820074925.ReMKUPP3@linutronix.de/ [1]
>>> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
>>> ---
>>>   drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
>>> index 31a17a56eb3b..25b1b699b3e2 100644
>>> --- a/drivers/perf/riscv_pmu_sbi.c
>>> +++ b/drivers/perf/riscv_pmu_sbi.c
>>> @@ -1373,11 +1373,15 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>>>
>>>        /* SBI PMU Snapsphot is only available in SBI v2.0 */
>>>        if (sbi_v2_available) {
>>> +             int cpu;
>>> +
>>>                ret = pmu_sbi_snapshot_alloc(pmu);
>>>                if (ret)
>>>                        goto out_unregister;
>>>
>>> -             ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
>>> +             cpu = get_cpu();
>>> +
>>> +             ret = pmu_sbi_snapshot_setup(pmu, cpu);
>>>                if (ret) {
>>>                        /* Snapshot is an optional feature. Continue if not available */
>>>                        pmu_sbi_snapshot_free(pmu);
>>> @@ -1391,6 +1395,7 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>>>                         */
>>>                        static_branch_enable(&sbi_pmu_snapshot_available);
>>>                }
>>> +             put_cpu();
>>
>> Are you sure it's safe to enable the static key with preemption disabled?
>> I thought that could block on a mutex.
> 

Thanks Will for pointing that out.

> Yep, it seems you're right, thanks for jumping in.
> 
> I'm discussing with Atish how to fix that differently, I'll be back
> with another version very soon.
> 

Looking at the driver core framework code, I am wondering if a probe 
function can be preempted to run on a different cpu. If it can only be 
preempted by higher priority kernel threads or interrupts but is 
guaranteed to run on the same cpu again, we can just use the 
raw_smp_processor_id.

However, if there is no guarantee then we can just invoke 
get_cpu/put_cpu around pmu_sbi_snapshot_setup.

> Thanks again,
> 
> Alex
> 
>>
>> Will
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
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