On 27 May 2016 at 12:41, Hoan Tran <hotran@xxxxxxx> wrote: > Hi Ashwin, Hi, > > 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 Just for future reference. :) https://web.archive.org/web/20080722025748/http://www.zip.com.au/~akpm/linux/patches/stuff/top-posting.txt > > On Fri, May 27, 2016 at 9:10 AM, Ashwin Chaugule > <ashwin.chaugule@xxxxxxxxxx> wrote: >> On 25 May 2016 at 15:09, Hoan Tran <hotran@xxxxxxx> 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 <hotran@xxxxxxx> >>> --- >>> 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. >> So, after freeing the cpc_ptr, we need to NULL the per-cpu pointer as well. Alternately, not assign it until everything passes and rely on the static declaration, which is the path you've taken here. Acked-by: Ashwin Chaugule <ashwin.chaugule@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
