powerpc/code-patching: Perform hwsync in __patch_instruction() in case of failure

Commit c28c15b6 ("powerpc/code-patching: Use temporary mm for
Radix MMU") added a hwsync for when __patch_instruction() fails,
we results in a quite odd unbalanced logic.

Instead of calling mb() when __patch_instruction() returns an error,
call mb() in the __patch_instruction()'s error path directly.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/e88b154eaf2efd9ff177d472d3411dcdec8ff4f5.1696675567.git.christophe.leroy@csgroup.eu

arch/powerpc/lib/code-patching.c

@@ -38,6 +38,7 @@ static int __patch_instruction(u32 *exec_addr, ppc_inst_t instr, u32 *patch_addr
 	return 0;
 
 failed:
+	mb();  /* sync */
 	return -EPERM;
 }
 
@@ -309,10 +310,6 @@ static int __do_patch_instruction_mm(u32 *addr, ppc_inst_t instr)
 
 	err = __patch_instruction(addr, instr, patch_addr);
 
-	/* hwsync performed by __patch_instruction (sync) if successful */
-	if (err)
-		mb();  /* sync */
-
 	/* context synchronisation performed by __patch_instruction (isync or exception) */
 	stop_using_temp_mm(patching_mm, orig_mm);