[PATCH] perf/core: Avoid removing shared pmu_context on unregister

[Chris Wilson]

In commit 1fd7e4169954 ("perf/core: Remove perf_cpu_context::unique_pmu"),
the search for another user of the pmu_cpu_context was removed, and so
we unconditionally free it during perf_pmu_unregister. This leads to
random corruption later and a BUG at mm/percpu.c:689.

Fixes: 1fd7e4169954 ("perf/core: Remove perf_cpu_context::unique_pmu")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.11+
---
 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index aaefaa27e1a6..e62b6207925c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9005,7 +9005,8 @@ void perf_pmu_unregister(struct pmu *pmu)
 		device_del(pmu->dev);
 		put_device(pmu->dev);
 	}
-	free_pmu_context(pmu);
+	if (!find_pmu_context(pmu->task_ctx_nr))
+		free_pmu_context(pmu);
 }
 EXPORT_SYMBOL_GPL(perf_pmu_unregister);
 
-- 
2.11.0