x86, bts: fix unlock problem in ds.c

Fix a problem where ds_request() returned an error without releasing the
ds lock.

Reported-by: Stephane Eranian <[e-mail]>
Signed-off-by: Markus Metzger <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/ds.c

···
 
 	spin_lock(&ds_lock);
 
+	error = -EPERM;
 	if (!check_tracer(task))
-		return -EPERM;
+		goto out_unlock;
 
 	error = -ENOMEM;
 	context = ds_alloc_context(task);