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

[Anju T Sudhakar <anju@linux.vnet.ibm.com>]

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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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