[PATCH] handle slip module unload race better.

[Stephen Hemminger <shemminger@xxxxxxxx>]

On Thu, 12 Jun 2003 14:58:03 -0700 (PDT)
"David S. Miller" <davem@xxxxxxxxxx> wrote:

>    From: Stephen Hemminger <shemminger@xxxxxxxx>
>    Date: Thu, 12 Jun 2003 13:27:14 -0700
> 
>    The following won't work.
>    
>  ...
>                               unregister_netdev(&slc->dev);
>                               if (slc->ctrl.tty) {
>                                       printk(KERN_ERR "%s: tty discipline is 
> still running\n", slc->dev.name);
>                                       /* Pin module forever */
>                                       MOD_INC_USE_COUNT;
>    
>    Because it is in the exit code for the module, and by that time
>    the module code has decided it is going to remove it and no
>    longer looks at the ref count.  Sorry, don't have a patch to
>    fix since this is related more to the problematic tty code, 
>    than the network code.
>    
> I think a reasonable thing for it to do is leak the netdevice
> and print a message when this happens.

Okay, this patch does that. I could start and unload slip, but could
not actually trigger the failure.

diff -Nru a/drivers/net/slip.c b/drivers/net/slip.c
--- a/drivers/net/slip.c        Thu Jun 12 16:10:30 2003
+++ b/drivers/net/slip.c        Thu Jun 12 16:10:30 2003
@@ -1381,27 +1381,23 @@
                        local_bh_enable();
                } while (busy && time_before(jiffies, timeout));
 
-               busy = 0;
                for (i = 0; i < slip_maxdev; i++) {
                        struct slip_ctrl *slc = slip_ctrls[i];
                        if (slc) {
                                unregister_netdev(&slc->dev);
                                if (slc->ctrl.tty) {
                                        printk(KERN_ERR "%s: tty discipline is 
still running\n", slc->dev.name);
-                                       /* Pin module forever */
-                                       MOD_INC_USE_COUNT;
-                                       busy++;
-                                       continue;
+                                       /* Intentionally leak the control 
block. */
+                               } else {
+                                       sl_free_bufs(&slc->ctrl);
+                                       kfree(slc);
                                }
-                               sl_free_bufs(&slc->ctrl);
-                               kfree(slc);
                                slip_ctrls[i] = NULL;
                        }
                }
-               if (!busy) {
-                       kfree(slip_ctrls);
-                       slip_ctrls = NULL;
-               }
+
+               kfree(slip_ctrls);
+               slip_ctrls = NULL;
        }
        if ((i = tty_register_ldisc(N_SLIP, NULL)))
        {