Hi Ashwin, Yes, I saw kernel crash. As cpc_desc_ptr is not NULL, cppc_cpufreq_init() still can pass then crash during cppc_get_perf_caps() access CPPC shared memory.
It's not only "PCC channel request fail" can create this issue but "acpi_get_psd() fail" also creates it Thanks Hoan On Fri, May 27, 2016 at 9:10 AM, Ashwin Chaugule <ashwin.chaug...@linaro.org> wrote: > On 25 May 2016 at 15:09, Hoan Tran <hot...@apm.com> wrote: >> When CPPC fails to request PCC channel, the CPC data is freed >> and cpc_desc_ptr points to the invalid data. This change prevents >> this issue by moving cpc_desc_ptr assignment after PCC channel >> request. >> >> Signed-off-by: Hoan Tran <hot...@apm.com> >> --- >> drivers/acpi/cppc_acpi.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c >> index 8adac69..85fd8f7 100644 >> --- a/drivers/acpi/cppc_acpi.c >> +++ b/drivers/acpi/cppc_acpi.c >> @@ -595,9 +595,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr) >> /* Store CPU Logical ID */ >> cpc_ptr->cpu_id = pr->id; >> >> - /* Plug it into this CPUs CPC descriptor. */ >> - per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr; >> - >> /* Parse PSD data for this CPU */ >> ret = acpi_get_psd(cpc_ptr, handle); >> if (ret) >> @@ -610,6 +607,9 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr) >> goto out_free; >> } >> >> + /* Plug PSD data into this CPUs CPC descriptor. */ >> + per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr; >> + > > Are you seeing a real problem without this change? I'm missing where > this pointer is dereferenced if the PCC channel request fails. > > Thanks, > Ashwin.
