On Sat, Jan 23, 2021 at 8:45 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> > > @@ -178,11 +182,23 @@ int lapb_unregister(struct net_device *dev)
> > > goto out;
> > > lapb_put(lapb);
> > >
> > > + /* Wait for other refs to "lapb" to drop */
> > > + while (refcount_read(&lapb->refcnt) > 2)
> > > + ;
>
> Tight loop like this is a little scary, perhaps add a small
> usleep_range() here?
OK, sure. I'll add a usleep_range(1, 10) here.
> > > -int lapb_disconnect_request(struct net_device *dev)
> > > +static int __lapb_disconnect_request(struct lapb_cb *lapb)
> > > {
> > > - struct lapb_cb *lapb = lapb_devtostruct(dev);
> > > - int rc = LAPB_BADTOKEN;
> > > -
> > > - if (!lapb)
> > > - goto out;
> > > -
> > > switch (lapb->state) {
> > > case LAPB_STATE_0:
> > > - rc = LAPB_NOTCONNECTED;
> > > - goto out_put;
> > > + return LAPB_NOTCONNECTED;
> > >
> > > case LAPB_STATE_1:
> > > lapb_dbg(1, "(%p) S1 TX DISC(1)\n", lapb->dev);
> > > @@ -310,12 +328,10 @@ int lapb_disconnect_request(struct net_device
> > > *dev)
> > > lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND);
> > > lapb->state = LAPB_STATE_0;
> > > lapb_start_t1timer(lapb);
> > > - rc = LAPB_NOTCONNECTED;
> > > - goto out_put;
> > > + return LAPB_NOTCONNECTED;
> > >
> > > case LAPB_STATE_2:
> > > - rc = LAPB_OK;
> > > - goto out_put;
> > > + return LAPB_OK;
> > > }
> > >
> > > lapb_clear_queues(lapb);
> > > @@ -328,8 +344,22 @@ int lapb_disconnect_request(struct net_device
> > > *dev)
> > > lapb_dbg(1, "(%p) S3 DISC(1)\n", lapb->dev);
> > > lapb_dbg(0, "(%p) S3 -> S2\n", lapb->dev);
> > >
> > > - rc = LAPB_OK;
> > > -out_put:
> > > + return LAPB_OK;
> > > +}
>
> Since this is a fix for net, I'd advise against converting the goto
> into direct returns (as much as I generally like such conversion).
This part is actually splitting "lapb_disconnect_request" into two
functions - a "__lapb_disconnect_request" without locking, and a
"lapb_disconnect_request" which provides the locking and calls
"__lapb_disconnect_request". The splitting is necessary for
"lapb_device_event" to directly call "__lapb_disconnect_request" with
the lock already held. After the splitting, the "out_put" tag would
actually be in the caller function so there's nowhere we can "goto".
