Re: [PATCH] powerpc: Make doorbell check preemption safe

[Shreyas B Prabhu]

On Wednesday 20 May 2015 06:30 AM, Michael Neuling wrote:
> On Wed, 2015-05-20 at 00:30 +0530, Shreyas B. Prabhu wrote:
>> Doorbell can be used to cause ipi on cpus which are sibling threads on
>> the same core. So icp_native_cause_ipi checks if the destination cpu
>> is a sibling thread of the current cpu and uses doorbell in such cases.
>>
>> But while running with CONFIG_PREEMPT=y, since this section is
>> preemtible, we can run into issues if after we check if the destination
>> cpu is a sibling cpu, the task gets migrated from a sibling cpu to a
>> cpu on another core.
>>
>> Fix this by using get_cpu()/ put_cpu()
> 
> Thanks.  Looks good and it's boots for me.
> 
> Signed-off-by: Michael Neuling 
> 
mikey, Thanks!


mpe, if this looks ok, can you please pick it up?

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Re: [PATCH] powerpc: Make doorbell check preemption safe

[Michael Neuling]

On Wed, 2015-05-20 at 00:30 +0530, Shreyas B. Prabhu wrote:
> Doorbell can be used to cause ipi on cpus which are sibling threads on
> the same core. So icp_native_cause_ipi checks if the destination cpu
> is a sibling thread of the current cpu and uses doorbell in such cases.
> 
> But while running with CONFIG_PREEMPT=y, since this section is
> preemtible, we can run into issues if after we check if the destination
> cpu is a sibling cpu, the task gets migrated from a sibling cpu to a
> cpu on another core.
> 
> Fix this by using get_cpu()/ put_cpu()

Thanks.  Looks good and it's boots for me.

Signed-off-by: Michael Neuling 

> Signed-off-by: Shreyas B. Prabhu 
> ---
>  arch/powerpc/sysdev/xics/icp-native.c | 14 +-
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/sysdev/xics/icp-native.c 
> b/arch/powerpc/sysdev/xics/icp-native.c
> index 2fc4cf1..62fd478 100644
> --- a/arch/powerpc/sysdev/xics/icp-native.c
> +++ b/arch/powerpc/sysdev/xics/icp-native.c
> @@ -147,12 +147,16 @@ static void icp_native_cause_ipi(int cpu, unsigned long 
> data)
>  {
>   kvmppc_set_host_ipi(cpu, 1);
>  #ifdef CONFIG_PPC_DOORBELL
> - if (cpu_has_feature(CPU_FTR_DBELL) &&
> - (cpumask_test_cpu(cpu, cpu_sibling_mask(smp_processor_id()
> - doorbell_cause_ipi(cpu, data);
> - else
> + if (cpu_has_feature(CPU_FTR_DBELL)) {
> + if (cpumask_test_cpu(cpu, cpu_sibling_mask(get_cpu( {
> + doorbell_cause_ipi(cpu, data);
> + put_cpu();
> + return;
> + }
> + put_cpu();
> + }
>  #endif
> - icp_native_set_qirr(cpu, IPI_PRIORITY);
> + icp_native_set_qirr(cpu, IPI_PRIORITY);
>  }
>  
>  /*

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[PATCH] powerpc: Make doorbell check preemption safe

[Shreyas B. Prabhu]

Doorbell can be used to cause ipi on cpus which are sibling threads on
the same core. So icp_native_cause_ipi checks if the destination cpu
is a sibling thread of the current cpu and uses doorbell in such cases.

But while running with CONFIG_PREEMPT=y, since this section is
preemtible, we can run into issues if after we check if the destination
cpu is a sibling cpu, the task gets migrated from a sibling cpu to a
cpu on another core.

Fix this by using get_cpu()/ put_cpu()

Signed-off-by: Shreyas B. Prabhu 
---
 arch/powerpc/sysdev/xics/icp-native.c | 14 +-
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/sysdev/xics/icp-native.c 
b/arch/powerpc/sysdev/xics/icp-native.c
index 2fc4cf1..62fd478 100644
--- a/arch/powerpc/sysdev/xics/icp-native.c
+++ b/arch/powerpc/sysdev/xics/icp-native.c
@@ -147,12 +147,16 @@ static void icp_native_cause_ipi(int cpu, unsigned long 
data)
 {
kvmppc_set_host_ipi(cpu, 1);
 #ifdef CONFIG_PPC_DOORBELL
-   if (cpu_has_feature(CPU_FTR_DBELL) &&
-   (cpumask_test_cpu(cpu, cpu_sibling_mask(smp_processor_id()
-   doorbell_cause_ipi(cpu, data);
-   else
+   if (cpu_has_feature(CPU_FTR_DBELL)) {
+   if (cpumask_test_cpu(cpu, cpu_sibling_mask(get_cpu( {
+   doorbell_cause_ipi(cpu, data);
+   put_cpu();
+   return;
+   }
+   put_cpu();
+   }
 #endif
-   icp_native_set_qirr(cpu, IPI_PRIORITY);
+   icp_native_set_qirr(cpu, IPI_PRIORITY);
 }
 
 /*
-- 
1.9.3

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