On Wed, Mar 04, 2015 at 04:49:15PM +0800, pi-cheng.chen wrote:
+static int cpu_opp_table_get_freq_index(unsigned int freq) +{
- struct cpu_opp_table *opp_tbl = dvfs_info->opp_tbl;
- int i;
- for (i = 0; opp_tbl[i].freq != 0; i++) {
if (opp_tbl[i].freq >= freq)return i;- }
- return -1;
My "return -1" detector fired on this...
+static int cpu_opp_table_get_volt_index(unsigned int volt) +{
- struct cpu_opp_table *opp_tbl = dvfs_info->opp_tbl;
- int i;
- for (i = 0; opp_tbl[i].vproc != -1; i++)
if (opp_tbl[i].vproc >= volt)return i;- return -1;
And this.
+static int mtk_cpufreq_notify(struct notifier_block *nb,
unsigned long action, void *data)+{
- struct cpufreq_freqs *freqs = data;
- struct cpu_opp_table *opp_tbl = dvfs_info->opp_tbl;
- int old_vproc, new_vproc, old_index, new_index;
- if (!cpumask_test_cpu(freqs->cpu, &dvfs_info->cpus))
return NOTIFY_DONE;- old_vproc = regulator_get_voltage(dvfs_info->proc_reg);
- old_index = cpu_opp_table_get_volt_index(old_vproc);
- new_index = cpu_opp_table_get_freq_index(freqs->new * 1000);
- new_vproc = opp_tbl[new_index].vproc;
Let's say that cpu_opp_table_get_freq_index() returns -1. We then do no error checking on this, and access the memory immediately preceding opp_tbl[0].
Since we'll be loading garbage from opp_tbl[-1], this probably means that mtk_cpufreq_voltage_trace() will go wrong. Your method of using the vproc values to work out which direction we should walk between old_index...new_index means that we could end up walking through almost the whole UINT_MAX range to wrap around to the new index.
Yet again, "return -1" proves to be a sure sign of a bug.