m68k: Handle 68040 bus faults

Fix 68040 bus fault handling, so the standard kernel exception handling
can be used for i/o probing.

Contrary to normal access faults there is nothing to fix, but at least
we have to disable writebacks to avoid recursive faults.
Signed-off-by: NRoman Zippel <zippel@linux-m68k.org>
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/m68k/kernel/traps.c

@@ -468,15 +468,26 @@ static inline void access_error040(struct frame *fp)
 			 * (if do_page_fault didn't fix the mapping,
                          * the writeback won't do good)
 			 */
+disable_wb:
 #ifdef DEBUG
 			printk(".. disabling wb2\n");
 #endif
 			if (fp->un.fmt7.wb2a == fp->un.fmt7.faddr)
 				fp->un.fmt7.wb2s &= ~WBV_040;
+			if (fp->un.fmt7.wb3a == fp->un.fmt7.faddr)
+				fp->un.fmt7.wb3s &= ~WBV_040;
 		}
-	} else if (send_fault_sig(&fp->ptregs) > 0) {
-		printk("68040 access error, ssw=%x\n", ssw);
-		trap_c(fp);
+	} else {
+		/* In case of a bus error we either kill the process or expect
+		 * the kernel to catch the fault, which then is also responsible
+		 * for cleaning up the mess.
+		 */
+		current->thread.signo = SIGBUS;
+		current->thread.faddr = fp->un.fmt7.faddr;
+		if (send_fault_sig(&fp->ptregs) >= 0)
+			printk("68040 bus error (ssw=%x, faddr=%lx)\n", ssw,
+			       fp->un.fmt7.faddr);
+		goto disable_wb;
 	}
 
 	do_040writebacks(fp);