[IA64] Correct convert_to_non_syscall()

convert_to_non_syscall() has the same problem that unwind_to_user()
used to have. Fix it likewise.

Signed-off-by: David Mosberger-Tang <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

arch/ia64/kernel/ptrace.c

···
 			unsigned long cfm)
 {
 	struct unw_frame_info info, prev_info;
-	unsigned long ip, pr;
+	unsigned long ip, sp, pr;
 
 	unw_init_from_blocked_task(&info, child);
 	while (1) {
 		prev_info = info;
 		if (unw_unwind(&info) < 0)
 			return;
-		if (unw_get_rp(&info, &ip) < 0)
+
+		unw_get_sp(&info, &sp);
+		if ((long)((unsigned long)child + IA64_STK_OFFSET - sp)
+		    < IA64_PT_REGS_SIZE) {
+			dprintk("ptrace.%s: ran off the top of the kernel "
+				"stack\n", __FUNCTION__);
 			return;
-		if (ip < FIXADDR_USER_END)
+		}
+		if (unw_get_pr (&prev_info, &pr) < 0) {
+			unw_get_rp(&prev_info, &ip);
+			dprintk("ptrace.%s: failed to read "
+				"predicate register (ip=0x%lx)\n",
+				__FUNCTION__, ip);
+			return;
+		}
+		if (unw_is_intr_frame(&info)
+		    && (pr & (1UL << PRED_USER_STACK)))
 			break;
 	}