sched_ext: Refactor lockup handlers into handle_lockup()

scx_rcu_cpu_stall() and scx_softlockup() share the same pattern: check if the
scheduler is enabled under RCU read lock and trigger an error if so. Extract
the common pattern into handle_lockup() helper. Add scx_verror() macro and use
guard(rcu)().

This simplifies both handlers, reduces code duplication, and prepares for
hardlockup handling.

Reviewed-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Cc: Emil Tsalapatis <etsal@meta.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: htejun

kernel/sched/ext.c

@@ -192,6 +192,7 @@ static __printf(4, 5) bool scx_exit(struct scx_sched *sch,
 }
 
 #define scx_error(sch, fmt, args...)	scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args)
+#define scx_verror(sch, fmt, args)	scx_vexit((sch), SCX_EXIT_ERROR, 0, fmt, args)
 
 #define SCX_HAS_OP(sch, op)	test_bit(SCX_OP_IDX(op), (sch)->has_op)
 
@@ -3654,39 +3655,40 @@ bool scx_allow_ttwu_queue(const struct task_struct *p)
 	return false;
 }
 
-/**
- * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler
- *
- * While there are various reasons why RCU CPU stalls can occur on a system
- * that may not be caused by the current BPF scheduler, try kicking out the
- * current scheduler in an attempt to recover the system to a good state before
- * issuing panics.
- */
-bool scx_rcu_cpu_stall(void)
+static __printf(1, 2) bool handle_lockup(const char *fmt, ...)
 {
 	struct scx_sched *sch;
+	va_list args;
 
-	rcu_read_lock();
+	guard(rcu)();
 
 	sch = rcu_dereference(scx_root);
-	if (unlikely(!sch)) {
-		rcu_read_unlock();
+	if (unlikely(!sch))
 		return false;
-	}
 
 	switch (scx_enable_state()) {
 	case SCX_ENABLING:
 	case SCX_ENABLED:
-		break;
+		va_start(args, fmt);
+		scx_verror(sch, fmt, args);
+		va_end(args);
+		return true;
 	default:
-		rcu_read_unlock();
 		return false;
 	}
+}
 
-	scx_error(sch, "RCU CPU stall detected!");
-	rcu_read_unlock();
-
-	return true;
+/**
+ * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler
+ *
+ * While there are various reasons why RCU CPU stalls can occur on a system
+ * that may not be caused by the current BPF scheduler, try kicking out the
+ * current scheduler in an attempt to recover the system to a good state before
+ * issuing panics.
+ */
+bool scx_rcu_cpu_stall(void)
+{
+	return handle_lockup("RCU CPU stall detected!");
 }
 
 /**
@@ -3701,28 +3703,11 @@ bool scx_rcu_cpu_stall(void)
  */
 void scx_softlockup(u32 dur_s)
 {
-	struct scx_sched *sch;
-
-	rcu_read_lock();
-
-	sch = rcu_dereference(scx_root);
-	if (unlikely(!sch))
-		goto out_unlock;
-
-	switch (scx_enable_state()) {
-	case SCX_ENABLING:
-	case SCX_ENABLED:
-		break;
-	default:
-		goto out_unlock;
-	}
-
-	printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU%d stuck for %us, disabling \"%s\"\n",
-			smp_processor_id(), dur_s, scx_root->ops.name);
+	if (!handle_lockup("soft lockup - CPU %d stuck for %us", smp_processor_id(), dur_s))
+		return;
 
-	scx_error(sch, "soft lockup - CPU#%d stuck for %us", smp_processor_id(), dur_s);
-out_unlock:
-	rcu_read_unlock();
+	printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n",
+			smp_processor_id(), dur_s);
 }
 
 /**