Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752241AbaFFPvm (ORCPT ); Fri, 6 Jun 2014 11:51:42 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37599 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751276AbaFFPvl (ORCPT ); Fri, 6 Jun 2014 11:51:41 -0400 Date: Fri, 6 Jun 2014 08:51:31 -0700 From: Greg Kroah-Hartman To: David Herrmann , Intel Graphics Development , Jiri Slaby , LKML , DRI Development Subject: Re: [PATCH 2/5] vt: Fix up unregistration of vt drivers Message-ID: <20140606155131.GB15110@kroah.com> References: <1401980308-5116-1-git-send-email-daniel.vetter@ffwll.ch> <1401980308-5116-2-git-send-email-daniel.vetter@ffwll.ch> <20140606075655.GC7416@phenom.ffwll.local> <20140606094050.GE7416@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140606094050.GE7416@phenom.ffwll.local> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 06, 2014 at 11:40:50AM +0200, Daniel Vetter wrote: > On Fri, Jun 06, 2014 at 10:47:25AM +0200, David Herrmann wrote: > > Hi > > > > On Fri, Jun 6, 2014 at 9:56 AM, Daniel Vetter wrote: > > > On Fri, Jun 06, 2014 at 09:24:35AM +0200, David Herrmann wrote: > > >> Hi > > >> > > >> On Thu, Jun 5, 2014 at 4:58 PM, Daniel Vetter wrote: > > >> > A bunch of issues: > > >> > - We should not kick out the default console (which is tracked in > > >> > conswitchp), so check for that. > > >> > - Add better error codes so callers can differentiate between "something > > >> > went wrong" and "your driver isn't registered already". i915 needs > > >> > that so it doesn't fall over when reloading the driver and hence > > >> > vga_con is already unregistered. > > >> > - There's a mess with the driver flags: What we need to check for is > > >> > that the driver isn't used any more, i.e. unbound completely (FLAG_INIT). > > >> > And not whether it's the boot console or not (which is the only one > > >> > which doesn't have FLAG_MODULE). Otherwise there's no way to kick > > >> > out the boot console, which i915 wants to do to prevent havoc with > > >> > vga_con interferring (which tends to hang machines). > > >> > > > >> > Cc: Greg Kroah-Hartman > > >> > Cc: Jiri Slaby > > >> > Signed-off-by: Daniel Vetter > > >> > --- > > >> > drivers/tty/vt/vt.c | 16 +++++++++------- > > >> > 1 file changed, 9 insertions(+), 7 deletions(-) > > >> > > > >> > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c > > >> > index ea600f482eeb..5077fe87324d 100644 > > >> > --- a/drivers/tty/vt/vt.c > > >> > +++ b/drivers/tty/vt/vt.c > > >> > @@ -3573,17 +3573,20 @@ err: > > >> > */ > > >> > int do_unregister_con_driver(const struct consw *csw) > > >> > { > > >> > - int i, retval = -ENODEV; > > >> > + int i; > > >> > > > >> > /* cannot unregister a bound driver */ > > >> > if (con_is_bound(csw)) > > >> > - goto err; > > >> > + return -EBUSY; > > >> > + > > >> > + if (csw == conswitchp) > > >> > + return -EINVAL; > > >> > > >> Ugh, that fix is correct, but I'd rather like to see > > >> do_unbind_con_driver() do the right thing. It currently resets > > >> conswitchp _only_ if the new fallback is unbound. Why not _always_ set > > >> conswitchp to defcsw _iff_ conswitchp == csw there? > > > > > > Ha, that's what I've thought, too. But do_unbind doesn't actually change > > > conswitchp, it only restores it because apparently the > > > vga_con->con_startup function is a real con and changes it behind > > > everyones back for no good reason. Or at least that's what the comment > > > claims. Note how defconsw != defcsw ... > > > > > > I've tried to follow around how conswitchp is actually used, but besides > > > that it's used to select the boot console I'm not sure at all what's going > > > hence. > > > > I missed that line: > > const struct consw *defconsw = conswitchp; > > > > Now that I looked at it again, this looks _really_ wrong. If > > conswitchp is vgacon and startup fails, we keep it set to vgacon.. > > ugh, weird. But ok, that's up to the people who wrote that. > > > > Btw., conswitchp is used for visual_init(), that is, every new VT > > allocation gets assigned to conswitchp. Therefore, it must be a valid > > driver. (VTs are allocated and deallocated by agetty/systemd after a > > session is started/ended). > > Ah, I missed where conswitchp was used in the maze, was getting a bit hazy > ;-) > > Rules for changing/updateing conswitchp are indeed a bit strange, which is > why I really don't want to touch this too much. > > > >> This way, you _know_ here that if !con_is_bound(csw), then csw != conswitchp. > > > > > > Hence why I dropped this approach again (I've done it originally) and > > > opted for the straightforward but albeit crude direct check. > > > > > >> > > > >> > for (i = 0; i < MAX_NR_CON_DRIVER; i++) { > > >> > struct con_driver *con_driver = ®istered_con_driver[i]; > > >> > > > >> > if (con_driver->con == csw && > > >> > - con_driver->flag & CON_DRIVER_FLAG_MODULE) { > > >> > + con_driver->flag & CON_DRIVER_FLAG_INIT) { > > >> > > >> That makes FLAG_MODULE almost a no-op except for ->unbind(). I wonder > > >> why FLAG_MODULE exists, anyway. > > > > > > I've dug around in git history and it's less than useful. It was renamed > > > from FLAG_BIND (which makes somewhat sense, since it roughly tracks > > > whether a console is bound). But there's never been a justification for > > > it, neither in the original patch nor in the one that renamed it. > > > > > > So I decided to not tempt fate and went with the small change here that > > > I've understood somewhat (I've tried other, more invasive changes and > > > failed). > > > > > >> Otherwise looks good. > > > > > > I'm really reluctant to do the right thing here since the code overall has > > > very unclear semantics with conswitchp and FLAG_MODULE. Can I convince > > > yout that the more direct approach here is the right one? > > > > Yeah, patch looks good. > > > > Reviewed-by: David Herrmann > > Thanks for the review. > > Greg, are you ok with these 3 vt patches and with me merging them through > drm-intel trees? We need them to properly kick out vgacon, which tends to > result in machine hangs (mostly across module reload, but also on driver > load on really unlucky systems) and other havoc. Yes, no objection from me at all, please feel free to add: Acked-by: Greg Kroah-Hartman to them. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/