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>

diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
index 620dcd405ff6eec9ae65b0af8e93c25daae15d1f..b32755679395dd20ce6ed9afc34f0dfd31a01173 100644 (file)
--- 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,