6.12-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 003659fec9f6d8c04738cb74b5384398ae8a7e88 ]
There is a fairly obvious race between perf_init_event() doing idr_find() and perf_pmu_register() doing idr_alloc() with an incompletely initialized PMU pointer.
Avoid by doing idr_alloc() on a NULL pointer to register the id, and swizzling the real struct pmu pointer at the end using idr_replace().
Also making sure to not set struct pmu members after publishing the struct pmu, duh.
[ introduce idr_cmpxchg() in order to better handle the idr_replace() error case -- if it were to return an unexpected pointer, it will already have replaced the value and there is no going back. ]
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20241104135517.858805880@infradead.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/core.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 5fff74c736063..cf2ec0a1582fd 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11737,6 +11737,21 @@ static int pmu_dev_alloc(struct pmu *pmu) static struct lock_class_key cpuctx_mutex; static struct lock_class_key cpuctx_lock;
+static bool idr_cmpxchg(struct idr *idr, unsigned long id, void *old, void *new) +{ + void *tmp, *val = idr_find(idr, id); + + if (val != old) + return false; + + tmp = idr_replace(idr, new, id); + if (IS_ERR(tmp)) + return false; + + WARN_ON_ONCE(tmp != val); + return true; +} + int perf_pmu_register(struct pmu *pmu, const char *name, int type) { int cpu, ret, max = PERF_TYPE_MAX; @@ -11763,7 +11778,7 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) if (type >= 0) max = type;
- ret = idr_alloc(&pmu_idr, pmu, max, 0, GFP_KERNEL); + ret = idr_alloc(&pmu_idr, NULL, max, 0, GFP_KERNEL); if (ret < 0) goto free_pdc;
@@ -11771,6 +11786,7 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
type = ret; pmu->type = type; + atomic_set(&pmu->exclusive_cnt, 0);
if (pmu_bus_running && !pmu->dev) { ret = pmu_dev_alloc(pmu); @@ -11819,14 +11835,22 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type) if (!pmu->event_idx) pmu->event_idx = perf_event_idx_default;
+ /* + * Now that the PMU is complete, make it visible to perf_try_init_event(). + */ + if (!idr_cmpxchg(&pmu_idr, pmu->type, NULL, pmu)) + goto free_context; list_add_rcu(&pmu->entry, &pmus); - atomic_set(&pmu->exclusive_cnt, 0); + ret = 0; unlock: mutex_unlock(&pmus_lock);
return ret;
+free_context: + free_percpu(pmu->cpu_pmu_context); + free_dev: if (pmu->dev && pmu->dev != PMU_NULL_DEV) { device_del(pmu->dev);