sched/core: Check for available DL bandwidth in cpuset_cpu_inactive()

Hotplug operations are destructive w.r.t. cpusets. In case such an
operation is performed on a CPU belonging to an exlusive cpuset, the
DL bandwidth information associated with the corresponding root
domain is gone even if the operation fails (in sched_cpu_inactive()).

For this reason we need to move the check we currently have in
sched_cpu_inactive() to cpuset_cpu_inactive() to prevent useless
cpusets reconfiguration in the CPU_DOWN_FAILED path.

Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Link: http://lkml.kernel.org/r/1427792017-7356-2-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4c49e75ca24dfdc1c4777cbe5960cbd5e08e3cde..28b0d75a82734f83c2975ae32b290d161022ee20 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5337,36 +5337,13 @@ static int sched_cpu_active(struct notifier_block *nfb,
 static int sched_cpu_inactive(struct notifier_block *nfb,
                                        unsigned long action, void *hcpu)
 {
-       unsigned long flags;
-       long cpu = (long)hcpu;
-       struct dl_bw *dl_b;
-
        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_DOWN_PREPARE:
-               set_cpu_active(cpu, false);
-
-               /* explicitly allow suspend */
-               if (!(action & CPU_TASKS_FROZEN)) {
-                       bool overflow;
-                       int cpus;
-
-                       rcu_read_lock_sched();
-                       dl_b = dl_bw_of(cpu);
-
-                       raw_spin_lock_irqsave(&dl_b->lock, flags);
-                       cpus = dl_bw_cpus(cpu);
-                       overflow = __dl_overflow(dl_b, cpus, 0, 0);
-                       raw_spin_unlock_irqrestore(&dl_b->lock, flags);
-
-                       rcu_read_unlock_sched();
-
-                       if (overflow)
-                               return notifier_from_errno(-EBUSY);
-               }
+               set_cpu_active((long)hcpu, false);
                return NOTIFY_OK;
+       default:
+               return NOTIFY_DONE;
        }
-
-       return NOTIFY_DONE;
 }
 
 static int __init migration_init(void)
@@ -7006,7 +6983,6 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
                 */
 
        case CPU_ONLINE:
-       case CPU_DOWN_FAILED:
                cpuset_update_active_cpus(true);
                break;
        default:
@@ -7018,8 +6994,32 @@ static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
 static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
                               void *hcpu)
 {
-       switch (action) {
+       unsigned long flags;
+       long cpu = (long)hcpu;
+       struct dl_bw *dl_b;
+
+       switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_DOWN_PREPARE:
+               /* explicitly allow suspend */
+               if (!(action & CPU_TASKS_FROZEN)) {
+                       bool overflow;
+                       int cpus;
+
+                       rcu_read_lock_sched();
+                       dl_b = dl_bw_of(cpu);
+
+                       raw_spin_lock_irqsave(&dl_b->lock, flags);
+                       cpus = dl_bw_cpus(cpu);
+                       overflow = __dl_overflow(dl_b, cpus, 0, 0);
+                       raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+
+                       rcu_read_unlock_sched();
+
+                       if (overflow) {
+                               trace_printk("hotplug failed for cpu %lu", cpu);
+                               return notifier_from_errno(-EBUSY);
+                       }
+               }
                cpuset_update_active_cpus(false);
                break;
        case CPU_DOWN_PREPARE_FROZEN: