s390/diag: avoid lockdep recursion

The diagnose tracer will indirectly call back into the lockdep code
when lockdep does not expect it (arch_spinlock). This causes lockdep
to disable itself and therefore we don't have a working lock
dependency validator anymore.

This patch effectively disables tracing of diag 0x9c and 0x44 if
lockdep is enabled.  If however lockdep is enabled spinlocks are
mainly implemented using a trylock variant, which will not issue any
diag 0x9c or 0x44. So this change has hardly any effect on tracing
except when arch_spinlock and friends are explicitly used.
Reported-and-Tested-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/trace.c

@@ -18,6 +18,9 @@ void trace_s390_diagnose_norecursion(int diag_nr)
 	unsigned long flags;
 	unsigned int *depth;
 
+	/* Avoid lockdep recursion. */
+	if (IS_ENABLED(CONFIG_LOCKDEP))
+		return;
 	local_irq_save(flags);
 	depth = this_cpu_ptr(&diagnose_trace_depth);
 	if (*depth == 0) {