Re: [REGRESSION][BISECT] perf/core: Remove pmu linear searching code

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Jun 05, 2023 at 11:27:31AM +0200, Peter Zijlstra wrote:

> That said; given that this commit has been tagged twice now, I suppose I
> should go revert it and we'll try again after a more thorough audit.

I'll go queue this then...

---
Subject: perf: Re-instate the linear PMU search
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon Jun  5 11:42:39 CEST 2023

Full revert of commit 9551fbb64d09 ("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 clean.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11630,27 +11630,38 @@ static struct pmu *perf_init_event(struc
 	}
 
 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;
+
+		ret = perf_try_init_event(pmu, event);
+		if (ret == -ENOENT && event->attr.type != type && !extended_type) {
+			type = event->attr.type;
+			goto again;
+		}
 
-	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;
+		if (ret)
+			pmu = ERR_PTR(ret);
+
+		goto unlock;
 	}
 
+	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:
-	if (ret)
-		pmu = ERR_PTR(ret);
-
+	pmu = ERR_PTR(-ENOENT);
 unlock:
 	srcu_read_unlock(&pmus_srcu, idx);