[GIT PULL] CPU hotplug fix

From: Ingo Molnar
Date: Sat Apr 23 2016 - 07:30:42 EST


Linus,

Please pull the latest smp-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git smp-urgent-for-linus

# HEAD: 3b9d6da67e11ca8f78fde887918983523a36b0fa cpu/hotplug: Fix rollback during error-out in __cpu_disable()

Fix a CPU hotplug corner case regression, introduced by the recent hotplug rework.

Thanks,

Ingo

------------------>
Sebastian Andrzej Siewior (1):
cpu/hotplug: Fix rollback during error-out in __cpu_disable()


kernel/cpu.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ea42e8da861..3e3f6e49eabb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -36,6 +36,7 @@
* @target: The target state
* @thread: Pointer to the hotplug thread
* @should_run: Thread should execute
+ * @rollback: Perform a rollback
* @cb_stat: The state for a single callback (install/uninstall)
* @cb: Single callback function (install/uninstall)
* @result: Result of the operation
@@ -47,6 +48,7 @@ struct cpuhp_cpu_state {
#ifdef CONFIG_SMP
struct task_struct *thread;
bool should_run;
+ bool rollback;
enum cpuhp_state cb_state;
int (*cb)(unsigned int cpu);
int result;
@@ -301,6 +303,11 @@ static int cpu_notify(unsigned long val, unsigned int cpu)
return __cpu_notify(val, cpu, -1, NULL);
}

+static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
+{
+ BUG_ON(cpu_notify(val, cpu));
+}
+
/* Notifier wrappers for transitioning to state machine */
static int notify_prepare(unsigned int cpu)
{
@@ -477,6 +484,16 @@ static void cpuhp_thread_fun(unsigned int cpu)
} else {
ret = cpuhp_invoke_callback(cpu, st->cb_state, st->cb);
}
+ } else if (st->rollback) {
+ BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
+
+ undo_cpu_down(cpu, st, cpuhp_ap_states);
+ /*
+ * This is a momentary workaround to keep the notifier users
+ * happy. Will go away once we got rid of the notifiers.
+ */
+ cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
+ st->rollback = false;
} else {
/* Cannot happen .... */
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
@@ -636,11 +653,6 @@ static inline void check_for_tasks(int dead_cpu)
read_unlock(&tasklist_lock);
}

-static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
-{
- BUG_ON(cpu_notify(val, cpu));
-}
-
static int notify_down_prepare(unsigned int cpu)
{
int err, nr_calls = 0;
@@ -721,9 +733,10 @@ static int takedown_cpu(unsigned int cpu)
*/
err = stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
if (err) {
- /* CPU didn't die: tell everyone. Can't complain. */
- cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
+ /* CPU refused to die */
irq_unlock_sparse();
+ /* Unpark the hotplug thread so we can rollback there */
+ kthread_unpark(per_cpu_ptr(&cpuhp_state, cpu)->thread);
return err;
}
BUG_ON(cpu_online(cpu));
@@ -832,6 +845,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
* to do the further cleanups.
*/
ret = cpuhp_down_callbacks(cpu, st, cpuhp_bp_states, target);
+ if (ret && st->state > CPUHP_TEARDOWN_CPU && st->state < prev_state) {
+ st->target = prev_state;
+ st->rollback = true;
+ cpuhp_kick_ap_work(cpu);
+ }

hasdied = prev_state != st->state && st->state == CPUHP_OFFLINE;
out:
@@ -1249,6 +1267,7 @@ static struct cpuhp_step cpuhp_ap_states[] = {
.name = "notify:online",
.startup = notify_online,
.teardown = notify_down_prepare,
+ .skip_onerr = true,
},
#endif
/*