From 180d86463257812dc17e5df912f3bddcc96abb00 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Tue, 11 Mar 2014 02:10:36 +0530 Subject: [PATCH] oprofile, nmi-timer: Fix CPU hotplug callback registration Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations). Instead, the correct and race-free way of performing the callback registration is: cpu_notifier_register_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_notifier_register_done(); Fix the nmi-timer code in oprofile by using this latter form of callback registration. Cc: Robert Richter Cc: Ingo Molnar Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- drivers/oprofile/nmi_timer_int.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/drivers/oprofile/nmi_timer_int.c b/drivers/oprofile/nmi_timer_int.c index 76f1c9357f39..9559829fb234 100644 --- a/drivers/oprofile/nmi_timer_int.c +++ b/drivers/oprofile/nmi_timer_int.c @@ -108,8 +108,8 @@ static void nmi_timer_shutdown(void) struct perf_event *event; int cpu; - get_online_cpus(); - unregister_cpu_notifier(&nmi_timer_cpu_nb); + cpu_notifier_register_begin(); + __unregister_cpu_notifier(&nmi_timer_cpu_nb); for_each_possible_cpu(cpu) { event = per_cpu(nmi_timer_events, cpu); if (!event) @@ -119,7 +119,7 @@ static void nmi_timer_shutdown(void) perf_event_release_kernel(event); } - put_online_cpus(); + cpu_notifier_register_done(); } static int nmi_timer_setup(void) @@ -132,20 +132,23 @@ static int nmi_timer_setup(void) do_div(period, HZ); nmi_timer_attr.sample_period = period; - get_online_cpus(); - err = register_cpu_notifier(&nmi_timer_cpu_nb); + cpu_notifier_register_begin(); + err = __register_cpu_notifier(&nmi_timer_cpu_nb); if (err) goto out; + /* can't attach events to offline cpus: */ for_each_online_cpu(cpu) { err = nmi_timer_start_cpu(cpu); - if (err) - break; + if (err) { + cpu_notifier_register_done(); + nmi_timer_shutdown(); + return err; + } } - if (err) - nmi_timer_shutdown(); + out: - put_online_cpus(); + cpu_notifier_register_done(); return err; }