From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754462AbaILOWE (ORCPT ); Fri, 12 Sep 2014 10:22:04 -0400 Received: from cantor2.suse.de ([195.135.220.15]:60308 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753991AbaILOWC (ORCPT ); Fri, 12 Sep 2014 10:22:02 -0400 Date: Fri, 12 Sep 2014 16:21:59 +0200 From: Petr Mladek To: Alan Stern Cc: Greg Kroah-Hartman , Tejun Heo , Joe Lawrence , Jiri Kosina , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] usb: hub: wrong order of putting interfaces when processing hub events Message-ID: <20140912142159.GA13354@pathway.suse.cz> References: <1410524421-15191-1-git-send-email-pmladek@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2014-09-12 10:06:03, Alan Stern wrote: > On Fri, 12 Sep 2014, Petr Mladek wrote: > > > usb_autopm_put_interface() must be called only when usb_autopm_get_interface() > > succeeded before. There was wrong ordering of the goto targets. > > No, you are wrong. The code is correct as it stands. > > > The funny thing is that the names of the goto targets and the related comments > > were correct. > > That's because the whole thing is correct. Go back and read the > comments more carefully -- especially the comment following the "loop:" > label. > > > Signed-off-by: Petr Mladek > > --- > > drivers/usb/core/hub.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c > > index d481c99a20d7..6afd79ee3340 100644 > > --- a/drivers/usb/core/hub.c > > +++ b/drivers/usb/core/hub.c > > @@ -5132,12 +5132,12 @@ static void hub_events(void) > > > > loop_autopm: > > /* Balance the usb_autopm_get_interface() above */ > > - usb_autopm_put_interface_no_suspend(intf); > > + usb_autopm_put_interface(intf); > > There's no point to this change. Now this call will decrement the > usage counter and try to suspend -- but the suspend is bound to fail > because the usage counter is still > 0. > > > loop: > > /* Balance the usb_autopm_get_interface_no_resume() in > > * kick_khubd() and allow autosuspend. > > */ > > - usb_autopm_put_interface(intf); > > + usb_autopm_put_interface_no_suspend(intf); > > And now this call will decrement the usage counter down to 0, but won't > try to suspend -- so the hub won't autosuspend at all! Ah, shame on me. It makes perfect sense. I was more focused on the kthread/workqueue conversion and function of the locks. I should have thought more about this as well :-( It means that the patchset "usb: hub: convert khubd into workqueue" needs refreshing. But I will wait for some feedback first. Best Regards, Petr