perf/core: Simplify perf_pmu_register()

Using the previously introduced perf_pmu_free() and a new IDR helper,
simplify the perf_pmu_register error paths.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20241104135518.198937277@infradead.org

include/linux/idr.h

@@ -15,6 +15,7 @@
 #include <linux/radix-tree.h>
 #include <linux/gfp.h>
 #include <linux/percpu.h>
+#include <linux/cleanup.h>
 
 struct idr {
 	struct radix_tree_root	idr_rt;
@@ -124,6 +125,22 @@ void *idr_get_next_ul(struct idr *, unsigned long *nextid);
 void *idr_replace(struct idr *, void *, unsigned long id);
 void idr_destroy(struct idr *);
 
+struct __class_idr {
+	struct idr *idr;
+	int id;
+};
+
+#define idr_null ((struct __class_idr){ NULL, -1 })
+#define take_idr_id(id) __get_and_null(id, idr_null)
+
+DEFINE_CLASS(idr_alloc, struct __class_idr,
+	     if (_T.id >= 0) idr_remove(_T.idr, _T.id),
+	     ((struct __class_idr){
+	     	.idr = idr,
+		.id = idr_alloc(idr, ptr, start, end, gfp),
+	     }),
+	     struct idr *idr, void *ptr, int start, int end, gfp_t gfp);
+
 /**
  * idr_init_base() - Initialise an IDR.
  * @idr: IDR handle.

kernel/events/core.c

@@ -11914,52 +11914,49 @@ static void perf_pmu_free(struct pmu *pmu)
 	free_percpu(pmu->cpu_pmu_context);
 }
 
-int perf_pmu_register(struct pmu *pmu, const char *name, int type)
+DEFINE_FREE(pmu_unregister, struct pmu *, if (_T) perf_pmu_free(_T))
+
+int perf_pmu_register(struct pmu *_pmu, const char *name, int type)
 {
-	int cpu, ret, max = PERF_TYPE_MAX;
+	int cpu, max = PERF_TYPE_MAX;
 
-	pmu->type = -1;
+	struct pmu *pmu __free(pmu_unregister) = _pmu;
+	guard(mutex)(&pmus_lock);
 
-	mutex_lock(&pmus_lock);
-	ret = -ENOMEM;
 	pmu->pmu_disable_count = alloc_percpu(int);
 	if (!pmu->pmu_disable_count)
-		goto unlock;
+		return -ENOMEM;
 
-	if (WARN_ONCE(!name, "Can not register anonymous pmu.\n")) {
-		ret = -EINVAL;
-		goto free;
-	}
+	if (WARN_ONCE(!name, "Can not register anonymous pmu.\n"))
+		return -EINVAL;
 
-	if (WARN_ONCE(pmu->scope >= PERF_PMU_MAX_SCOPE, "Can not register a pmu with an invalid scope.\n")) {
-		ret = -EINVAL;
-		goto free;
-	}
+	if (WARN_ONCE(pmu->scope >= PERF_PMU_MAX_SCOPE,
+		      "Can not register a pmu with an invalid scope.\n"))
+		return -EINVAL;
 
 	pmu->name = name;
 
 	if (type >= 0)
 		max = type;
 
-	ret = idr_alloc(&pmu_idr, NULL, max, 0, GFP_KERNEL);
-	if (ret < 0)
-		goto free;
+	CLASS(idr_alloc, pmu_type)(&pmu_idr, NULL, max, 0, GFP_KERNEL);
+	if (pmu_type.id < 0)
+		return pmu_type.id;
 
-	WARN_ON(type >= 0 && ret != type);
+	WARN_ON(type >= 0 && pmu_type.id != type);
 
-	pmu->type = ret;
+	pmu->type = pmu_type.id;
 	atomic_set(&pmu->exclusive_cnt, 0);
 
 	if (pmu_bus_running && !pmu->dev) {
-		ret = pmu_dev_alloc(pmu);
+		int ret = pmu_dev_alloc(pmu);
 		if (ret)
-			goto free;
+			return ret;
 	}
 
-	ret = -ENOMEM;
 	pmu->cpu_pmu_context = alloc_percpu(struct perf_cpu_pmu_context);
 	if (!pmu->cpu_pmu_context)
-		goto free;
+		return -ENOMEM;
 
 	for_each_possible_cpu(cpu) {
 		struct perf_cpu_pmu_context *cpc;
@@ -12000,32 +11997,22 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
 	/*
 	 * Now that the PMU is complete, make it visible to perf_try_init_event().
 	 */
-	if (!idr_cmpxchg(&pmu_idr, pmu->type, NULL, pmu)) {
-		ret = -EINVAL;
-		goto free;
-	}
+	if (!idr_cmpxchg(&pmu_idr, pmu->type, NULL, pmu))
+		return -EINVAL;
 	list_add_rcu(&pmu->entry, &pmus);
 
-	ret = 0;
-unlock:
-	mutex_unlock(&pmus_lock);
-
-	return ret;
-
-free:
-	if (pmu->type >= 0)
-		idr_remove(&pmu_idr, pmu->type);
-	perf_pmu_free(pmu);
-	goto unlock;
+	take_idr_id(pmu_type);
+	_pmu = no_free_ptr(pmu); // let it rip
+	return 0;
 }
 EXPORT_SYMBOL_GPL(perf_pmu_register);
 
 void perf_pmu_unregister(struct pmu *pmu)
 {
-	mutex_lock(&pmus_lock);
-	list_del_rcu(&pmu->entry);
-	idr_remove(&pmu_idr, pmu->type);
-	mutex_unlock(&pmus_lock);
+	scoped_guard (mutex, &pmus_lock) {
+		list_del_rcu(&pmu->entry);
+		idr_remove(&pmu_idr, pmu->type);
+	}
 
 	/*
 	 * We dereference the pmu list under both SRCU and regular RCU, so