um: print info about fatal segfaults

Print a short info about fatal segfaults like other archs do.
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/trap.c

@@ -113,6 +113,27 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 	return 0;
 }
 
+static void show_segv_info(struct uml_pt_regs *regs)
+{
+	struct task_struct *tsk = current;
+	struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+	if (!unhandled_signal(tsk, SIGSEGV))
+		return;
+
+	if (!printk_ratelimit())
+		return;
+
+	printk("%s%s[%d]: segfault at %lx ip %p sp %p error %x",
+		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
+		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
+		fi->error_code);
+
+	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
+	printk(KERN_CONT "\n");
+}
+
 static void bad_segv(struct faultinfo fi, unsigned long ip)
 {
 	struct siginfo si;
@@ -141,6 +162,7 @@ void segv_handler(int sig, struct uml_pt_regs *regs)
 	struct faultinfo * fi = UPT_FAULTINFO(regs);
 
 	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
+		show_segv_info(regs);
 		bad_segv(*fi, UPT_IP(regs));
 		return;
 	}
@@ -202,6 +224,8 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 		      address, ip);
 	}
 
+	show_segv_info(regs);
+
 	if (err == -EACCES) {
 		si.si_signo = SIGBUS;
 		si.si_errno = 0;