On 10 March 2015 at 00:28, Russell King - ARM Linux
[off-list ref] wrote:

On Wed, Mar 04, 2015 at 04:49:15PM +0800, pi-cheng.chen wrote:

quoted

+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...

quoted

+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.

quoted

+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.

Hi Russell,

Thanks for your reviewing. I'll fix it in next version.

Best Regards,
Pi-Cheng

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