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.
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according to speedtest.net.
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