[PATCH] powerpc/perf: Fix IMC allocation routine

[PATCH] powerpc/perf: Fix IMC allocation routine

[Guilherme G. Piccoli]

When setting nr_cpus=1, we observed a crash in IMC code during boot
due to a missing allocation: basically, IMC code is taking the number
of threads into account in imc_mem_init() and if we manually set
nr_cpus for a value that is not multiple of the number of threads per
core, an integer division in that function will discard the decimal
portion, leading IMC to not allocate one mem_info struct. This causes
a NULL pointer dereference later, on is_core_imc_mem_inited().

This patch just rounds that division up, fixing the bug.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
---
Anju, looks good to you? Tested in P9 with latest FW available.

 arch/powerpc/perf/imc-pmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 88126245881b..92ae5de0bbac 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -1104,7 +1104,7 @@ static int init_nest_pmu_ref(void)
 
 static void cleanup_all_core_imc_memory(void)
 {
-	int i, nr_cores = num_present_cpus() / threads_per_core;
+	int i, nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
 	struct imc_mem_info *ptr = core_imc_pmu->mem_info;
 	int size = core_imc_pmu->counter_mem_size;
 
@@ -1212,7 +1212,7 @@ static int imc_mem_init(struct imc_pmu *pmu_ptr, struct device_node *parent,
 		if (!pmu_ptr->pmu.name)
 			return -ENOMEM;
 
-		nr_cores = num_present_cpus() / threads_per_core;
+		nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
 		pmu_ptr->mem_info = kcalloc(nr_cores, sizeof(struct imc_mem_info),
 								GFP_KERNEL);
 
-- 
2.14.2

Re: [PATCH] powerpc/perf: Fix IMC allocation routine

[Anju T Sudhakar]

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Hi Guilherme,

Nice catch.

On Friday 20 October 2017 01:11 AM, Guilherme G. Piccoli wrote:
> When setting nr_cpus=1, we observed a crash in IMC code during boot
> due to a missing allocation: basically, IMC code is taking the number
> of threads into account in imc_mem_init() and if we manually set
> nr_cpus for a value that is not multiple of the number of threads per
> core, an integer division in that function will discard the decimal
> portion, leading IMC to not allocate one mem_info struct. This causes
> a NULL pointer dereference later, on is_core_imc_mem_inited().
>
> This patch just rounds that division up, fixing the bug.
>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Acked-by:  Anju T Sudhakar <anju@linux.vnet.ibm.com>
> ---
> Anju, looks good to you? Tested in P9 with latest FW available.
>
>   arch/powerpc/perf/imc-pmu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
> index 88126245881b..92ae5de0bbac 100644
> --- a/arch/powerpc/perf/imc-pmu.c
> +++ b/arch/powerpc/perf/imc-pmu.c
> @@ -1104,7 +1104,7 @@ static int init_nest_pmu_ref(void)
>
>   static void cleanup_all_core_imc_memory(void)
>   {
> -	int i, nr_cores = num_present_cpus() / threads_per_core;
> +	int i, nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
>   	struct imc_mem_info *ptr = core_imc_pmu->mem_info;
>   	int size = core_imc_pmu->counter_mem_size;
>
> @@ -1212,7 +1212,7 @@ static int imc_mem_init(struct imc_pmu *pmu_ptr, struct device_node *parent,
>   		if (!pmu_ptr->pmu.name)
>   			return -ENOMEM;
>
> -		nr_cores = num_present_cpus() / threads_per_core;
> +		nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
>   		pmu_ptr->mem_info = kcalloc(nr_cores, sizeof(struct imc_mem_info),
>   								GFP_KERNEL);
>

Thanks,
Anju

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Re: [PATCH] powerpc/perf: Fix IMC allocation routine

[Guilherme G. Piccoli]

On 10/24/2017 06:34 AM, Anju T Sudhakar wrote:
> Hi Guilherme,
> 
> Nice catch.
> 
> On Friday 20 October 2017 01:11 AM, Guilherme G. Piccoli wrote:
>> When setting nr_cpus=1, we observed a crash in IMC code during boot
>> due to a missing allocation: basically, IMC code is taking the number
>> of threads into account in imc_mem_init() and if we manually set
>> nr_cpus for a value that is not multiple of the number of threads per
>> core, an integer division in that function will discard the decimal
>> portion, leading IMC to not allocate one mem_info struct. This causes
>> a NULL pointer dereference later, on is_core_imc_mem_inited().
>>
>> This patch just rounds that division up, fixing the bug.
>>
>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
> Acked-by:  Anju T Sudhakar <anju@linux.vnet.ibm.com>

Thanks Anju :)

>> ---
>> Anju, looks good to you? Tested in P9 with latest FW available.
>>
>>  arch/powerpc/perf/imc-pmu.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
>> index 88126245881b..92ae5de0bbac 100644
>> --- a/arch/powerpc/perf/imc-pmu.c
>> +++ b/arch/powerpc/perf/imc-pmu.c
>> @@ -1104,7 +1104,7 @@ static int init_nest_pmu_ref(void)
>>
>>  static void cleanup_all_core_imc_memory(void)
>>  {
>> -	int i, nr_cores = num_present_cpus() / threads_per_core;
>> +	int i, nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
>>  	struct imc_mem_info *ptr = core_imc_pmu->mem_info;
>>  	int size = core_imc_pmu->counter_mem_size;
>>
>> @@ -1212,7 +1212,7 @@ static int imc_mem_init(struct imc_pmu *pmu_ptr, struct device_node *parent,
>>  		if (!pmu_ptr->pmu.name)
>>  			return -ENOMEM;
>>
>> -		nr_cores = num_present_cpus() / threads_per_core;
>> +		nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
>>  		pmu_ptr->mem_info = kcalloc(nr_cores, sizeof(struct imc_mem_info),
>>  								GFP_KERNEL);
>>
> 
> Thanks,
> Anju

Re: powerpc/perf: Fix IMC allocation routine

[Michael Ellerman]

On Thu, 2017-10-19 at 19:41:33 UTC, "Guilherme G. Piccoli" wrote:
> When setting nr_cpus=1, we observed a crash in IMC code during boot
> due to a missing allocation: basically, IMC code is taking the number
> of threads into account in imc_mem_init() and if we manually set
> nr_cpus for a value that is not multiple of the number of threads per
> core, an integer division in that function will discard the decimal
> portion, leading IMC to not allocate one mem_info struct. This causes
> a NULL pointer dereference later, on is_core_imc_mem_inited().
> 
> This patch just rounds that division up, fixing the bug.
> 
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/0b167f11085a34281349f395d20005

cheers