perf: Re-instate the linear PMU search

Full revert of commit 9551fbb6 ("perf/core: Remove pmu linear
searching code").

Some architectures (notably arm/arm64) still relied on the linear
search in order to find the PMU that consumes
PERF_TYPE_{HARDWARE,HW_CACHE,RAW}.

This will need a more thorought audit and cleanup.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230605101401.GL38236@hirez.programming.kicks-ass.net

kernel/events/core.c

@@ -11630,27 +11630,38 @@ static struct pmu *perf_init_event(struct perf_event *event)
 	}
 
 again:
-	ret = -ENOENT;
 	rcu_read_lock();
 	pmu = idr_find(&pmu_idr, type);
 	rcu_read_unlock();
-	if (!pmu)
-		goto fail;
+	if (pmu) {
+		if (event->attr.type != type && type != PERF_TYPE_RAW &&
+		    !(pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE))
+			goto fail;
 
-	if (event->attr.type != type && type != PERF_TYPE_RAW &&
-	    !(pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE))
-		goto fail;
+		ret = perf_try_init_event(pmu, event);
+		if (ret == -ENOENT && event->attr.type != type && !extended_type) {
+			type = event->attr.type;
+			goto again;
+		}
 
-	ret = perf_try_init_event(pmu, event);
-	if (ret == -ENOENT && event->attr.type != type && !extended_type) {
-		type = event->attr.type;
-		goto again;
+		if (ret)
+			pmu = ERR_PTR(ret);
+
+		goto unlock;
 	}
 
-fail:
-	if (ret)
-		pmu = ERR_PTR(ret);
+	list_for_each_entry_rcu(pmu, &pmus, entry, lockdep_is_held(&pmus_srcu)) {
+		ret = perf_try_init_event(pmu, event);
+		if (!ret)
+			goto unlock;
 
+		if (ret != -ENOENT) {
+			pmu = ERR_PTR(ret);
+			goto unlock;
+		}
+	}
+fail:
+	pmu = ERR_PTR(-ENOENT);
 unlock:
 	srcu_read_unlock(&pmus_srcu, idx);