Revert "powerpc/rtas: Warn if per-function lock isn't held"

This reverts commit 0298609 due to a
boot-time oops:

BUG: Kernel NULL pointer dereference on read at 0x00000018
Faulting instruction address: 0xc00000000004223c
Oops: Kernel access of bad area, sig: 7 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Tainted: G        W          6.6.0-rc2+ torvalds#129
NIP:  c00000000004223c LR: c000000000042238 CTR: 0000000000000000
REGS: c000000002c579d0 TRAP: 0300   Tainted: G        W           (6.6.0-rc2+)
MSR:  8000000000001033 <SF,ME,IR,DR,RI,LE>  CR: 28000284  XER: 00000000
CFAR: c000000000042008 DAR: 0000000000000018 DSISR: 00080000 IRQMASK: 3
GPR00: c000000000042238 c000000002c57c70 c000000001f5eb00 0000000000000000
GPR04: c00000000294cd08 0000000000000002 c000000002c579b4 0000000000000000
GPR08: 0000000000000000 0000000000000002 c000000002c0da80 0000000000000000
GPR12: 0000000000000000 c000000005e40000 0000000000000000 0000000002097728
GPR16: 0000000000001111 0000000000000001 0000000002097b80 00000000020975b8
GPR20: 00000000020976f0 00000000020974e8 00000000030feb00 00000000030feb00
GPR24: 0000000000002008 0000000000000000 0000000000000001 c0000000028f3d70
GPR28: 0000000002d31020 c000000002cac268 c000000002d31020 0000000000000000
NIP [c00000000004223c] do_enter_rtas+0xcc/0x460
LR [c000000000042238] do_enter_rtas+0xc8/0x460
Call Trace:
[c000000002c57c70] [c000000000042238] do_enter_rtas+0xc8/0x460 (unreliable)
[c000000002c57cc0] [c000000000042e34] rtas_call+0x434/0x490
[c000000002c57d20] [c0000000000fd584] papr_sysparm_get+0xe4/0x230
[c000000002c57db0] [c0000000020267d0] pSeries_probe+0x2f0/0x5fc
[c000000002c57e80] [c00000000200a318] setup_arch+0x11c/0x524
[c000000002c57f10] [c00000000200418c] start_kernel+0xcc/0xc1c
[c000000002c57fe0] [c00000000000e788] start_here_common+0x1c/0x20

arch/powerpc/kernel/rtas.c

@@ -670,25 +670,28 @@ static void __do_enter_rtas(struct rtas_args *args)
 
 static void __do_enter_rtas_trace(struct rtas_args *args)
 {
-	struct rtas_function *func = rtas_token_to_function(be32_to_cpu(args->token));
+	const char *name = NULL;
 
+	if (args == &rtas_args)
+		lockdep_assert_held(&rtas_lock);
 	/*
-	 * If there is a per-function lock, it must be held by the
-	 * caller.
+	 * If the tracepoints that consume the function name aren't
+	 * active, avoid the lookup.
 	 */
-	if (func->lock)
-		WARN_ON(!mutex_is_locked(func->lock));
+	if ((trace_rtas_input_enabled() || trace_rtas_output_enabled())) {
+		const s32 token = be32_to_cpu(args->token);
+		const struct rtas_function *func = rtas_token_to_function(token);
 
-	if (args == &rtas_args)
-		lockdep_assert_held(&rtas_lock);
+		name = func->name;
+	}
 
-	trace_rtas_input(args, func->name);
+	trace_rtas_input(args, name);
 	trace_rtas_ll_entry(args);
 
 	__do_enter_rtas(args);
 
 	trace_rtas_ll_exit(args);
-	trace_rtas_output(args, func->name);
+	trace_rtas_output(args, name);
 }
 
 static void do_enter_rtas(struct rtas_args *args)