linux-kernel - Re: 2.6.27-rc4: 90% system time because of khubd, unable to reboot

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Date:	Fri, 22 Aug 2008 20:29:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrey Borzenkov <arvidjaar@...l.ru>
Cc:	Alan Stern <stern@...land.harvard.edu>, linux-usb@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>
Subject: Re: 2.6.27-rc4: 90% system time because of khubd, unable to reboot

On Friday, 22 of August 2008, Andrey Borzenkov wrote:
> On Friday 22 August 2008, Alan Stern wrote:
> > On Fri, 22 Aug 2008, Andrey Borzenkov wrote:
> > 
> > > > > reverting 38b375d9610e2467cb793a84d17c6f65e44cdb39 fixed it
> > > > > 
> > > > 
> > > > ... that is:
> > > > 
> > > > commit 38b375d9610e2467cb793a84d17c6f65e44cdb39
> > > > Author: Alan Stern <stern@...land.harvard.edu>
> > > > Date:   Mon Jul 21 09:56:26 2008 -0400
> > > > 
> > > >     USB: OHCI: fix system hang caused by earlier patch
> > > > 
> > > >     Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > > >     Tested by: Andrey Borzenkov <arvidjaar@...l.ru>
> > > >     Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> > > > 
> > > > so it apparently used to work for you at that time.  What gives?
> > > > 
> > > 
> > > Well, you should not commit a fix without commiting code that has been
> > > fixed first :)
> > 
> > Actually the code to be fixed _was_ committed first -- but then it was 
> > reverted before the fix was accepted, so the fix was merged without it.
> > 
> > My advice is not to worry about it.  That code has been sent once again
> > to Linus -- it's not merged yet but presumably it will be soon.  
> > Certainly before 2.6.27-rc5 appears.
> > 
> > On the other hand, I still have to wonder how the fix could have caused
> > your problem without the original patch in place.  The fix itself
> > should have been totally innocuous.
> > 
> 
> It looks even funnier. Right now I am running with commits
> 38b375d9610e2467cb793a84d17c6f65e44cdb39 *and*
> e872154921a6b5256a3c412dd69158ac0b135176 reverted. I.e. this should be
> the state which hopelessly failed in 2.6.26-rc. It seems to be doing
> quite well now in 2.6.27-rc.
> 
> "git revert e872154921a6b5256a3c412dd69158ac0b135176" gives me this
> one liner patch:
> 
> commit f3cf9ad86ee76077d1c6be9af7d197aa13ccdff9
> Author: Andrey Borzenkov <arvidjaar@...l.ru>
> Date:   Fri Aug 22 21:15:26 2008 +0400
> 
>     Revert "USB: don't explicitly reenable root-hub status interrupts"
> 
>     This reverts commit e872154921a6b5256a3c412dd69158ac0b135176.
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 107e1d2..d30f822 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -3086,6 +3086,11 @@ static void hub_events(void)
>                 if (!hdev->parent && !hub->busy_bits[0])
>                         usb_enable_root_hub_irq(hdev->bus);
> 
> +               /* If this is a root hub, tell the HCD it's okay to
> +                * re-enable port-change interrupts now. */
> +               if (!hdev->parent && !hub->busy_bits[0])
> +                       usb_enable_root_hub_irq(hdev->bus);
> +
>  loop_autopm:
>                 /* Allow autosuspend if we're not going to run again */
>                 if (list_empty(&hub->event_list))
> 
> Either my git tree is completely botched or most parts were already reverted
> before.
> 
> So the problem seems to have cured by itself between 2.6.26 and 2.6.27?  

Well, such things happened in the past.

I won't add this to the list of regressions for now, but please monitor the
status of -rc5 and let me know if the problem reappears in there.

Thanks,
Rafael

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