thermal: cpu_cooling: don't call kcalloc() under rcu_read_lock

build_dyn_power_table() allocates the power table while holding
rcu_read_lock.  kcalloc using GFP_KERNEL may sleep, so it can't be
called in an RCU read-side path.

Move the rcu protection to the part of the function that really needs
it: the part that handles the dev_pm_opp pointer received from
dev_pm_opp_find_freq_ceil().  In the unlikely case that there is an OPP
added to the cpu while this function is running, return -EAGAIN.

Fixes: c36cf0717631 ("thermal: cpu_cooling: implement the power cooling device API")
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

1 files changed, 23 insertions, 24 deletions

diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
index 620dcd405ff6..b32755679395 100644
--- a/drivers/thermal/cpu_cooling.c
+++ b/drivers/thermal/cpu_cooling.c
@@ -262,7 +262,9 @@ static int cpufreq_thermal_notifier(struct notifier_block *nb,
  * efficiently.  Power is stored in mW, frequency in KHz.  The
  * resulting table is in ascending order.
  *
- * Return: 0 on success, -E* on error.
+ * Return: 0 on success, -EINVAL if there are no OPPs for any CPUs,
+ * -ENOMEM if we run out of memory or -EAGAIN if an OPP was
+ * added/enabled while the function was executing.
  */
 static int build_dyn_power_table(struct cpufreq_cooling_device *cpufreq_device,
                                  u32 capacitance)
@@ -270,11 +272,9 @@ static int build_dyn_power_table(struct cpufreq_cooling_device *cpufreq_device,
         struct power_table *power_table;
         struct dev_pm_opp *opp;
         struct device *dev = NULL;
-        int num_opps = 0, cpu, i, ret = 0;
+        int num_opps = 0, cpu, i;
         unsigned long freq;
 
-        rcu_read_lock();
-
         for_each_cpu(cpu, &cpufreq_device->allowed_cpus) {
                 dev = get_cpu_device(cpu);
                 if (!dev) {
@@ -284,24 +284,20 @@ static int build_dyn_power_table(struct cpufreq_cooling_device *cpufreq_device,
                 }
 
                 num_opps = dev_pm_opp_get_opp_count(dev);
-                if (num_opps > 0) {
+                if (num_opps > 0)
                         break;
-                } else if (num_opps < 0) {
-                        ret = num_opps;
-                        goto unlock;
-                }
+                else if (num_opps < 0)
+                        return num_opps;
         }
 
-        if (num_opps == 0) {
-                ret = -EINVAL;
-                goto unlock;
-        }
+        if (num_opps == 0)
+                return -EINVAL;
 
         power_table = kcalloc(num_opps, sizeof(*power_table), GFP_KERNEL);
-        if (!power_table) {
-                ret = -ENOMEM;
-                goto unlock;
-        }
+        if (!power_table)
+                return -ENOMEM;
+
+        rcu_read_lock();
 
         for (freq = 0, i = 0;
              opp = dev_pm_opp_find_freq_ceil(dev, &freq), !IS_ERR(opp);
@@ -309,6 +305,11 @@ static int build_dyn_power_table(struct cpufreq_cooling_device *cpufreq_device,
                 u32 freq_mhz, voltage_mv;
                 u64 power;
 
+                if (i >= num_opps) {
+                        rcu_read_unlock();
+                        return -EAGAIN;
+                }
+
                 freq_mhz = freq / 1000000;
                 voltage_mv = dev_pm_opp_get_voltage(opp) / 1000;
 
@@ -326,18 +327,16 @@ static int build_dyn_power_table(struct cpufreq_cooling_device *cpufreq_device,
                 power_table[i].power = power;
         }
 
-        if (i == 0) {
-                ret = PTR_ERR(opp);
-                goto unlock;
-        }
+        rcu_read_unlock();
+
+        if (i != num_opps)
+                return PTR_ERR(opp);
 
         cpufreq_device->cpu_dev = dev;
         cpufreq_device->dyn_power_table = power_table;
         cpufreq_device->dyn_power_table_entries = i;
 
-unlock:
-        rcu_read_unlock();
-        return ret;
+        return 0;
 }
 
 static u32 cpu_freq_to_power(struct cpufreq_cooling_device *cpufreq_device,