[PATCH 3.16 288/328] perf/core: Fix perf_pmu_unregister() locking

Ben Hutchings
2018-12-09T22:04:14Z

From: Peter Zijlstra <peterz@infradead.org>

commit a9f9772114c8b07ae75bcb3654bd017461248095 upstream.

When we unregister a PMU, we fail to serialize the @pmu_idr properly.
Fix that by doing the entire thing under pmu_lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 2e80a82a49c4 ("perf: Dynamic pmu types")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[bwh: Backported to 3.16:
- Also remove "out" label in free_pmu_context()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6705,20 +6705,17 @@ static void free_pmu_context(struct pmu
{
struct pmu *i;

- mutex_lock(&pmus_lock);
/*
* Like a real lame refcount.
*/
list_for_each_entry(i, &pmus, entry) {
if (i->pmu_cpu_context == pmu->pmu_cpu_context) {
update_pmu_context(i, pmu);
- goto out;
+ return;
}
}

free_percpu(pmu->pmu_cpu_context);
-out:
- mutex_unlock(&pmus_lock);
}
static struct idr pmu_idr;

@@ -6930,12 +6927,8 @@ EXPORT_SYMBOL_GPL(perf_pmu_register);

void perf_pmu_unregister(struct pmu *pmu)
{
- int remove_device;
-
mutex_lock(&pmus_lock);
- remove_device = pmu_bus_running;
list_del_rcu(&pmu->entry);
- mutex_unlock(&pmus_lock);

/*
* We dereference the pmu list under both SRCU and regular RCU, so
@@ -6947,11 +6940,12 @@ void perf_pmu_unregister(struct pmu *pmu
free_percpu(pmu->pmu_disable_count);
if (pmu->type >= PERF_TYPE_MAX)
idr_remove(&pmu_idr, pmu->type);
- if (remove_device) {
+ if (pmu_bus_running) {
device_del(pmu->dev);
put_device(pmu->dev);
}
free_pmu_context(pmu);
+ mutex_unlock(&pmus_lock);
}
EXPORT_SYMBOL_GPL(perf_pmu_unregister);