From: Alan Stern 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 Cc: "Paul E. McKenney" Cc: Jesse Brandeburg Cc: Dave Jones Signed-off-by: Andrew Morton --- drivers/cpufreq/cpufreq.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff -puN drivers/cpufreq/cpufreq.c~cpufreq-make-the-transition_notifier-chain-use-srcu drivers/cpufreq/cpufreq.c --- a/drivers/cpufreq/cpufreq.c~cpufreq-make-the-transition_notifier-chain-use-srcu +++ a/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; case CPUFREQ_POLICY_NOTIFIER: _