powerpc/perf: Fix IMC allocation routine

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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index 8812624..92ae5de 100644 (file)
--- 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);