Revert "n_gsm: race between ld close and gsmtty open"

This reverts commit c284ee2cf12b55fa8496b2d098bf0938688f1c1c.  Turns out
the locking was incorrect.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Chao Bi <chao.bi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 27 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 069bfd654485..c0f76da55304 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2054,11 +2054,9 @@ void gsm_cleanup_mux(struct gsm_mux *gsm)
                                         dlci->state == DLCI_CLOSED);
         }
         /* Free up any link layer users */
-        spin_lock(&gsm->lock);
         for (i = 0; i < NUM_DLCI; i++)
                 if (gsm->dlci[i])
                         gsm_dlci_release(gsm->dlci[i]);
-        spin_unlock(&gsm->lock);
         /* Now wipe the queues */
         list_for_each_entry_safe(txq, ntxq, &gsm->tx_list, list)
                 kfree(txq);
@@ -2911,33 +2909,23 @@ static int gsmtty_install(struct tty_driver *driver, struct tty_struct *tty)
         This is ok from a locking
         perspective as we don't have to worry about this
         if DLCI0 is lost */
-        spin_lock(&gsm->lock);
-        if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN) {
-                spin_unlock(&gsm->lock);
+        if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN)
                 return -EL2NSYNC;
-        }
         dlci = gsm->dlci[line];
         if (dlci == NULL) {
                 alloc = true;
                 dlci = gsm_dlci_alloc(gsm, line);
         }
-        if (dlci == NULL) {
-                spin_unlock(&gsm->lock);
+        if (dlci == NULL)
                 return -ENOMEM;
-        }
         ret = tty_port_install(&dlci->port, driver, tty);
         if (ret) {
                 if (alloc)
                         dlci_put(dlci);
-                spin_unlock(&gsm->lock);
                 return ret;
         }
 
-        dlci_get(dlci);
-        dlci_get(gsm->dlci[0]);
-        mux_get(gsm);
         tty->driver_data = dlci;
-        spin_unlock(&gsm->lock);
 
         return 0;
 }
@@ -2948,6 +2936,9 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
         struct tty_port *port = &dlci->port;
 
         port->count++;
+        dlci_get(dlci);
+        dlci_get(dlci->gsm->dlci[0]);
+        mux_get(dlci->gsm);
         tty_port_tty_set(port, tty);
 
         dlci->modem_rx = 0;
@@ -2974,7 +2965,7 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp)
         mutex_unlock(&dlci->mutex);
         gsm = dlci->gsm;
         if (tty_port_close_start(&dlci->port, tty, filp) == 0)
-                return;
+                goto out;
         gsm_dlci_begin_close(dlci);
         if (test_bit(ASYNCB_INITIALIZED, &dlci->port.flags)) {
                 if (C_HUPCL(tty))
@@ -2982,7 +2973,10 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp)
         }
         tty_port_close_end(&dlci->port, tty);
         tty_port_tty_set(&dlci->port, NULL);
-        return;
+out:
+        dlci_put(dlci);
+        dlci_put(gsm->dlci[0]);
+        mux_put(gsm);
 }
 
 static void gsmtty_hangup(struct tty_struct *tty)
@@ -3159,16 +3153,6 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state)
         return gsmtty_modem_update(dlci, encode);
 }
 
-static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
-{
-        struct gsm_dlci *dlci = tty->driver_data;
-        struct gsm_mux *gsm = dlci->gsm;
-
-        dlci_put(dlci);
-        dlci_put(gsm->dlci[0]);
-        mux_put(gsm);
-        driver->ttys[tty->index] = NULL;
-}
 
 /* Virtual ttys for the demux */
 static const struct tty_operations gsmtty_ops = {
@@ -3188,7 +3172,6 @@ static const struct tty_operations gsmtty_ops = {
         .tiocmget               = gsmtty_tiocmget,
         .tiocmset               = gsmtty_tiocmset,
         .break_ctl              = gsmtty_break_ctl,
-        .remove                 = gsmtty_remove,
 };