[PATCH] cpufreq: make the transition_notifier chain use SRCU

This patch (as762) changes the cpufreq_transition_notifier_list from a
blocking_notifier_head to an srcu_notifier_head.  This will prevent errors
caused attempting to call down_read() to access the notifier chain at a
time when interrupts must remain disabled, during system suspend.

It's not clear to me whether this is really necessary; perhaps the chain
could be made into an atomic_notifier.  However a couple of the callout
routines do use blocking operations, so this approach seems safer.

The head of the notifier chain needs to be initialized before use; this is
done by an __init routine at core_initcall time.  If this turns out not to
be a good choice, it can easily be changed.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Jesse Brandeburg <jesse.brandeburg@gmail.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 13 insertions, 7 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2caaf71d80c8..86e69b7f9122 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -52,8 +52,14 @@ static void handle_update(void *data);
  * The mutex locks both lists.
  */
 static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
-static BLOCKING_NOTIFIER_HEAD(cpufreq_transition_notifier_list);
+static struct srcu_notifier_head cpufreq_transition_notifier_list;
 
+static int __init init_cpufreq_transition_notifier_list(void)
+{
+        srcu_init_notifier_head(&cpufreq_transition_notifier_list);
+        return 0;
+}
+core_initcall(init_cpufreq_transition_notifier_list);
 
 static LIST_HEAD(cpufreq_governor_list);
 static DEFINE_MUTEX (cpufreq_governor_mutex);
@@ -262,14 +268,14 @@ void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
                                 freqs->old = policy->cur;
                         }
                 }
-                blocking_notifier_call_chain(&cpufreq_transition_notifier_list,
+                srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
                                 CPUFREQ_PRECHANGE, freqs);
                 adjust_jiffies(CPUFREQ_PRECHANGE, freqs);
                 break;
 
         case CPUFREQ_POSTCHANGE:
                 adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
-                blocking_notifier_call_chain(&cpufreq_transition_notifier_list,
+                srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
                                 CPUFREQ_POSTCHANGE, freqs);
                 if (likely(policy) && likely(policy->cpu == freqs->cpu))
                         policy->cur = freqs->new;
@@ -1049,7 +1055,7 @@ static int cpufreq_suspend(struct sys_device * sysdev, pm_message_t pmsg)
                 freqs.old = cpu_policy->cur;
                 freqs.new = cur_freq;
 
-                blocking_notifier_call_chain(&cpufreq_transition_notifier_list,
+                srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
                                     CPUFREQ_SUSPENDCHANGE, &freqs);
                 adjust_jiffies(CPUFREQ_SUSPENDCHANGE, &freqs);
 
@@ -1130,7 +1136,7 @@ static int cpufreq_resume(struct sys_device * sysdev)
                         freqs.old = cpu_policy->cur;
                         freqs.new = cur_freq;
 
-                        blocking_notifier_call_chain(
+                        srcu_notifier_call_chain(
                                         &cpufreq_transition_notifier_list,
                                         CPUFREQ_RESUMECHANGE, &freqs);
                         adjust_jiffies(CPUFREQ_RESUMECHANGE, &freqs);
@@ -1176,7 +1182,7 @@ int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list)
 
         switch (list) {
         case CPUFREQ_TRANSITION_NOTIFIER:
-                ret = blocking_notifier_chain_register(
+                ret = srcu_notifier_chain_register(
                                 &cpufreq_transition_notifier_list, nb);
                 break;
         case CPUFREQ_POLICY_NOTIFIER:
@@ -1208,7 +1214,7 @@ int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list)
 
         switch (list) {
         case CPUFREQ_TRANSITION_NOTIFIER:
-                ret = blocking_notifier_chain_unregister(
+                ret = srcu_notifier_chain_unregister(
                                 &cpufreq_transition_notifier_list, nb);
                 break;
         case CPUFREQ_POLICY_NOTIFIER: