perf/core: Exit early on perf_mmap() fail

When perf_mmap() fails to allocate a buffer, it still invokes the
event_mapped() callback of the related event. On X86 this might increase
the perf_rdpmc_allowed reference counter. But nothing undoes this as
perf_mmap_close() is never called in this case, which causes another
reference count leak.

Return early on failure to prevent that.

Fixes: 1e0fb9ec679c ("perf: Add pmu callbacks to track event mapping and unmapping")
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Lorenzo Stoakes <[e-mail]>
Cc: [e-mail]

kernel/events/core.c

···
 		mutex_unlock(aux_mutex);
 	mutex_unlock(&event->mmap_mutex);
 
+	if (ret)
+		return ret;
+
 	/*
 	 * Since pinned accounting is per vm we cannot allow fork() to copy our
 	 * vma.
···
 	vm_flags_set(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP);
 	vma->vm_ops = &perf_mmap_vmops;
 
-	if (!ret)
-		ret = map_range(rb, vma);
+	ret = map_range(rb, vma);
 
 	mapped = get_mapped(event, event_mapped);
 	if (mapped)