perf/core: Exit early on perf_mmap() fail

commit 07091aade3 upstream.

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: 1e0fb9ec67 ("perf/core: Add pmu callbacks to track event mapping and unmapping")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/events/core.c

@@ -6003,6 +6003,9 @@ unlock:
 aux_unlock:
 	mutex_unlock(&event->mmap_mutex);
 
+	if (ret)
+		return ret;
+
 	/*
 	 * Since pinned accounting is per vm we cannot allow fork() to copy our
 	 * vma.