Blackfin: finish_atomic_sections: optimize the RTS step

No point in returning to userspace just to have it immediately perform the
RTS step.  We have to update the PC anyways, so do the RTS too.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/kernel/process.c

@@ -258,59 +258,63 @@ void finish_atomic_sections (struct pt_regs *regs)
 	int __user *up0 = (int __user *)regs->p0;
 
 	switch (regs->pc) {
+	default:
+		/* not in middle of an atomic step, so resume like normal */
+		return;
+
 	case ATOMIC_XCHG32 + 2:
 		put_user(regs->r1, up0);
-		regs->pc = ATOMIC_XCHG32 + 4;
 		break;
 
 	case ATOMIC_CAS32 + 2:
 	case ATOMIC_CAS32 + 4:
 		if (regs->r0 == regs->r1)
 	case ATOMIC_CAS32 + 6:
 			put_user(regs->r2, up0);
-		regs->pc = ATOMIC_CAS32 + 8;
 		break;
 
 	case ATOMIC_ADD32 + 2:
 		regs->r0 = regs->r1 + regs->r0;
 		/* fall through */
 	case ATOMIC_ADD32 + 4:
 		put_user(regs->r0, up0);
-		regs->pc = ATOMIC_ADD32 + 6;
 		break;
 
 	case ATOMIC_SUB32 + 2:
 		regs->r0 = regs->r1 - regs->r0;
 		/* fall through */
 	case ATOMIC_SUB32 + 4:
 		put_user(regs->r0, up0);
-		regs->pc = ATOMIC_SUB32 + 6;
 		break;
 
 	case ATOMIC_IOR32 + 2:
 		regs->r0 = regs->r1 | regs->r0;
 		/* fall through */
 	case ATOMIC_IOR32 + 4:
 		put_user(regs->r0, up0);
-		regs->pc = ATOMIC_IOR32 + 6;
 		break;
 
 	case ATOMIC_AND32 + 2:
 		regs->r0 = regs->r1 & regs->r0;
 		/* fall through */
 	case ATOMIC_AND32 + 4:
 		put_user(regs->r0, up0);
-		regs->pc = ATOMIC_AND32 + 6;
 		break;
 
 	case ATOMIC_XOR32 + 2:
 		regs->r0 = regs->r1 ^ regs->r0;
 		/* fall through */
 	case ATOMIC_XOR32 + 4:
 		put_user(regs->r0, up0);
-		regs->pc = ATOMIC_XOR32 + 6;
 		break;
 	}
+
+	/*
+	 * We've finished the atomic section, and the only thing left for
+	 * userspace is to do a RTS, so we might as well handle that too
+	 * since we need to update the PC anyways.
+	 */
+	regs->pc = regs->rets;
 }
 
 static inline