On Wed, 31 Aug 2011 20:08:45 +0000 (UTC) Naga Chumbalkar <nagananda.chumbalkar@xxxxxx> wrote: > If, for whatever reason, "pr" ends up being NULL we would end up in a PANIC > as seen below: > > Loading CPUFreq modules[ 437.661360] BUG: unable to handle kernel NULL pointer > dereference at (null) > IP: [<ffffffffa0434314>] pcc_cpufreq_cpu_init+0x74/0x220 [pcc_cpufreq] > > It's better to prevent the PANIC by failing the driver, and allowing the system to boot. > > Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@xxxxxx> > Cc: stable@xxxxxxxxxx > > diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c > index 7b0603e..cdc02ac 100644 > --- a/drivers/cpufreq/pcc-cpufreq.c > +++ b/drivers/cpufreq/pcc-cpufreq.c > @@ -261,6 +261,9 @@ static int pcc_get_offset(int cpu) > pr = per_cpu(processors, cpu); > pcc_cpu_data = per_cpu_ptr(pcc_cpu_info, cpu); > > + if (!pr) > + return -ENODEV; > + > status = acpi_evaluate_object(pr->handle, "PCCP", NULL, &buffer); > if (ACPI_FAILURE(status)) > return -ENODEV; hm, from reading drivers/acpi/processor_driver.c it appears that per_cpu(processors, n)==NULL is an expected and valid state. Heaven knows what that state actually *means* - apparently this is a secret. I assume that you've hit this crash in real live code, hence your suggestion of a -stable backport? -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
