linux-kernel - [PATCH v2] cpu/hotplug: Do not bail-out in DYING/STARTING sections

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Date:   Mon, 23 May 2022 17:05:36 +0100
From:   Vincent Donnefort <vdonnefort@...gle.com>
To:     peterz@...radead.org, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, vschneid@...hat.com,
        kernel-team@...roid.com, Vincent Donnefort <vdonnefort@...gle.com>,
        Derek Dolney <z23@...teo.net>
Subject: [PATCH v2] cpu/hotplug: Do not bail-out in DYING/STARTING sections

The DYING/STARTING callbacks are not expected to fail. However, as reported
by Derek, drivers such as tboot are still free to return errors within
those sections. In that case, there's nothing the hotplug machinery can do,
so let's just proceed and log the failures.

Fixes: 453e41085183 (cpu/hotplug: Add cpuhp_invoke_callback_range())
Reported-by: Derek Dolney <z23@...teo.net>
Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>

---

v1 -> v2: 
   - Commit message rewording.
   - More details in the warnings.
   - Some variable renaming

diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..c3617683459e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -663,21 +663,51 @@ static bool cpuhp_next_state(bool bringup,
 	return true;
 }
 
-static int cpuhp_invoke_callback_range(bool bringup,
-				       unsigned int cpu,
-				       struct cpuhp_cpu_state *st,
-				       enum cpuhp_state target)
+static int _cpuhp_invoke_callback_range(bool bringup,
+					unsigned int cpu,
+					struct cpuhp_cpu_state *st,
+					enum cpuhp_state target,
+					bool nofail)
 {
 	enum cpuhp_state state;
-	int err = 0;
+	int ret = 0;
 
 	while (cpuhp_next_state(bringup, &state, st, target)) {
+		int err;
+
 		err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
-		if (err)
+		if (!err)
+			continue;
+
+		if (nofail) {
+			pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
+				cpu, bringup ? "UP" : "DOWN",
+				cpuhp_get_step(st->state)->name,
+				st->state, err);
+			ret = -1;
+		} else {
+			ret = err;
 			break;
+		}
 	}
 
-	return err;
+	return ret;
+}
+
+static inline int cpuhp_invoke_callback_range(bool bringup,
+					      unsigned int cpu,
+					      struct cpuhp_cpu_state *st,
+					      enum cpuhp_state target)
+{
+	return _cpuhp_invoke_callback_range(bringup, cpu, st, target, false);
+}
+
+static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
+						      unsigned int cpu,
+						      struct cpuhp_cpu_state *st,
+						      enum cpuhp_state target)
+{
+	WARN_ON_ONCE(_cpuhp_invoke_callback_range(bringup, cpu, st, target, true));
 }
 
 static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
@@ -999,7 +1029,6 @@ static int take_cpu_down(void *_param)
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
 	int err, cpu = smp_processor_id();
-	int ret;
 
 	/* Ensure this CPU doesn't handle any more interrupts. */
 	err = __cpu_disable();
@@ -1012,13 +1041,11 @@ static int take_cpu_down(void *_param)
 	 */
 	WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
 
-	/* Invoke the former CPU_DYING callbacks */
-	ret = cpuhp_invoke_callback_range(false, cpu, st, target);
-
 	/*
+	 * Invoke the former CPU_DYING callbacks
 	 * DYING must not fail!
 	 */
-	WARN_ON_ONCE(ret);
+	cpuhp_invoke_callback_range_nofail(false, cpu, st, target);
 
 	/* Give up timekeeping duties */
 	tick_handover_do_timer();
@@ -1296,16 +1323,14 @@ void notify_cpu_starting(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 	enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
-	int ret;
 
 	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
 	cpumask_set_cpu(cpu, &cpus_booted_once_mask);
-	ret = cpuhp_invoke_callback_range(true, cpu, st, target);
 
 	/*
 	 * STARTING must not fail!
 	 */
-	WARN_ON_ONCE(ret);
+	cpuhp_invoke_callback_range_nofail(true, cpu, st, target);
 }
 
 /*
-- 
2.36.1.124.g0e6072fb45-goog