From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 4 Nov 2024 13:39:11 +0000 (+0100)
Subject: perf/core: Fix pmus_lock vs. pmus_srcu ordering
X-Git-Tag: v6.14-rc6~17^2~1
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=2565e42539b120b81a68a58da961ce5d1e34eac8;p=linux-block.git

perf/core: Fix pmus_lock vs. pmus_srcu ordering

Commit a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order")
placed pmus_lock inside pmus_srcu, this makes perf_pmu_unregister()
trip lockdep.

Move the locking about such that only pmu_idr and pmus (list) are
modified while holding pmus_lock. This avoids doing synchronize_srcu()
while holding pmus_lock and all is well again.

Fixes: a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20241104135517.679556858@infradead.org
---

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6364319e2f88..11793d690cbb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11939,6 +11939,8 @@ 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);
 
 	/*
 	 * We dereference the pmu list under both SRCU and regular RCU, so
@@ -11948,7 +11950,6 @@ void perf_pmu_unregister(struct pmu *pmu)
 	synchronize_rcu();
 
 	free_percpu(pmu->pmu_disable_count);
-	idr_remove(&pmu_idr, pmu->type);
 	if (pmu_bus_running && pmu->dev && pmu->dev != PMU_NULL_DEV) {
 		if (pmu->nr_addr_filters)
 			device_remove_file(pmu->dev, &dev_attr_nr_addr_filters);
@@ -11956,7 +11957,6 @@ void perf_pmu_unregister(struct pmu *pmu)
 		put_device(pmu->dev);
 	}
 	free_pmu_context(pmu);
-	mutex_unlock(&pmus_lock);
 }
 EXPORT_SYMBOL_GPL(perf_pmu_unregister);