[PATCH 2/2] cpufreq: make the transition_notifier chain use SRCU

Alan Stern
2006-08-02T20:38:36Z

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>

---

Index: 2.6.18-rc2-mm1/drivers/cpufreq/cpufreq.c
===================================================================
--- 2.6.18-rc2-mm1.orig/drivers/cpufreq/cpufreq.c
+++ 2.6.18-rc2-mm1/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 cp
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_de
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_dev
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 not

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 n

switch (list) {
case CPUFREQ_TRANSITION_NOTIFIER:
- ret = blocking_notifier_chain_unregister(
+ ret = srcu_notifier_chain_unregister(
&cpufreq_transition_notifier_list, nb);
break;