[src/trunk]: src/sys/kern Provide consistent locking around getc() in ttread(...

[mlelstv <mlelstv%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b8031a5f6b79
branches:  trunk
changeset: 781781:b8031a5f6b79
user:      mlelstv <mlelstv%NetBSD.org@localhost>
date:      Sun Sep 30 11:49:44 2012 +0000

description:
Provide consistent locking around getc() in ttread(). This is necessary
to prevent crashes in MPSAFE tty drivers like ucom.

diffstat:

 sys/kern/tty.c |  13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

diffs (58 lines):

diff -r cd5bec781682 -r b8031a5f6b79 sys/kern/tty.c
--- a/sys/kern/tty.c    Sun Sep 30 11:29:42 2012 +0000
+++ b/sys/kern/tty.c    Sun Sep 30 11:49:44 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tty.c,v 1.253 2012/08/17 16:21:19 christos Exp $       */
+/*     $NetBSD: tty.c,v 1.254 2012/09/30 11:49:44 mlelstv Exp $        */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -63,7 +63,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.253 2012/08/17 16:21:19 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.254 2012/09/30 11:49:44 mlelstv Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1928,7 +1928,6 @@
                goto loop;
        }
  read:
-       mutex_spin_exit(&tty_lock);
 
        /*
         * Input present, check for input mapping and processing.
@@ -1940,16 +1939,14 @@
                 */
                if (CCEQ(cc[VDSUSP], c) &&
                    ISSET(lflag, IEXTEN|ISIG) == (IEXTEN|ISIG)) {
-                       mutex_spin_enter(&tty_lock);
                        ttysig(tp, TTYSIG_PG1, SIGTSTP);
                        if (first) {
                                error = ttypause(tp, hz);
-                               mutex_spin_exit(&tty_lock);
                                if (error)
                                        break;
+                               mutex_spin_exit(&tty_lock);
                                goto loop;
-                       } else
-                               mutex_spin_exit(&tty_lock);
+                       }
                        break;
                }
                /*
@@ -1973,11 +1970,11 @@
                        break;
                first = 0;
        }
+
        /*
         * Look to unblock output now that (presumably)
         * the input queue has gone down.
         */
-       mutex_spin_enter(&tty_lock);
        if (ISSET(tp->t_state, TS_TBLOCK) && tp->t_rawq.c_cc < TTYHOG / 5) {
                if (ISSET(tp->t_iflag, IXOFF) &&
                    cc[VSTART] != _POSIX_VDISABLE &&