powerpc/interrupt: Do not call single_step_exception() from other exceptions

single_step_exception() is called by emulate_single_step() which
is called from (at least) alignment exception() handler and
program_check_exception() handler.

Redefine it as a regular __single_step_exception() which is called
by both single_step_exception() handler and emulate_single_step()
function.

Fixes: 3a96570f ("powerpc: convert interrupt handlers to use wrappers")
Cc: stable@vger.kernel.org # v5.12+
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/aed174f5cbc06f2cf95233c071d8aac948e46043.1628611921.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/traps.c

@@ -1104,7 +1104,7 @@ DEFINE_INTERRUPT_HANDLER(RunModeException)
 	_exception(SIGTRAP, regs, TRAP_UNK, 0);
 }
 
-DEFINE_INTERRUPT_HANDLER(single_step_exception)
+static void __single_step_exception(struct pt_regs *regs)
 {
 	clear_single_step(regs);
 	clear_br_trace(regs);
@@ -1121,6 +1121,11 @@ DEFINE_INTERRUPT_HANDLER(single_step_exception)
 	_exception(SIGTRAP, regs, TRAP_TRACE, regs->nip);
 }
 
+DEFINE_INTERRUPT_HANDLER(single_step_exception)
+{
+	__single_step_exception(regs);
+}
+
 /*
  * After we have successfully emulated an instruction, we have to
  * check if the instruction was being single-stepped, and if so,
@@ -1130,7 +1135,7 @@ DEFINE_INTERRUPT_HANDLER(single_step_exception)
 static void emulate_single_step(struct pt_regs *regs)
 {
 	if (single_stepping(regs))
-		single_step_exception(regs);
+		__single_step_exception(regs);
 }
 
 static inline int __parse_fpscr(unsigned long fpscr)