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

Alexandre Ghiti posted 1 patch 1 year, 3 months ago
There is a newer version of this series
drivers/perf/riscv_pmu_sbi.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
[PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code
Posted by Alexandre Ghiti 1 year, 3 months ago 
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
Posted by Will Deacon 1 year, 3 months ago 
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
Posted by Alexandre Ghiti 1 year, 3 months ago 
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
Posted by Atish Patra 1 year, 3 months ago 
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
> http://lists.infradead.org/mailman/listinfo/linux-riscv
Re: [PATCH -fixes] drivers: perf: Fix smp_processor_id() use in preemptible code
Posted by Andrea Parri 1 year, 3 months ago 
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
Posted by Alexandre Ghiti 1 year, 3 months ago 
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
Posted by Nam Cao 1 year, 3 months ago 
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
Posted by Alexandre Ghiti 1 year, 3 months ago 
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
Posted by Anup Patel 1 year, 3 months ago 
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
>

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