linux-kernel - Re: [bug] hung bootup in various drivers, was: "2.6.21-rc5: known regressions"

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Date:	Fri, 30 Mar 2007 12:32:58 -0700
From:	Greg KH <gregkh@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Kay Sievers <kay.sievers@...y.org>, Adrian Bunk <bunk@...sta.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [bug] hung bootup in various drivers, was: "2.6.21-rc5: known
	regressions"

On Fri, Mar 30, 2007 at 07:46:19PM +0200, Ingo Molnar wrote:
> 
> * Greg KH <gregkh@...e.de> wrote:
> 
> > >  BUG: at drivers/base/driver.c:187 driver_unregister()
> > >   [<c0105ff9>] show_trace_log_lvl+0x19/0x2e
> > >   [<c01063e2>] show_trace+0x12/0x14
> > >   [<c01063f8>] dump_stack+0x14/0x16
> > >   [<c063f7e6>] driver_unregister+0x3d/0x43
> > >   [<c0488048>] pci_unregister_driver+0x10/0x5f
> > >   [<c1b5f7c7>] slgt_init+0x9b/0x1ca
> > >   [<c1b31a2d>] init+0x15d/0x2bd
> > >   [<c0105bc3>] kernel_thread_helper+0x7/0x10
> 
> > Yes, we should allow the ability to call unregister_driver from within 
> > the module_init function.
> > 
> > But I don't understand what is causing you to see this problem.  Who 
> > is holding the reference on the struct device at this point in time?  
> > Is it the fact that userspace has some files open and it hasn't 
> > released them yet?
> 
> at least in the slgt_init() case the affected codepath is trivial:
> 
>         if ((rc = pci_register_driver(&pci_driver)) < 0) {
>                 printk("%s pci_register_driver error=%d\n", driver_name, rc);
>                 return rc;
>         }
>         pci_registered = 1;
> 
>         if (!slgt_device_list) {
>                 printk("%s no devices found\n",driver_name);
>                 pci_unregister_driver(&pci_driver);
>                 return -ENODEV;
> 
> slgt_device_list is NULL because no matching PCI ID is on my system (i 
> dont have this hardware), so the ->probe() function did not get called 
> at all.

Sorry, no, I realize how this could happen in the driver, I just don't
see what in the driver core would be keeping this driver from having
it's release function called at the unregister() time.

Something has grabbed a reference to the driver...

Oh wait, is this code a module or built into the kernel?

If it's built in, there's still a reference counting bug in the
module/driver hookup logic as we really don't have a "module" yet we are
still thinking we do as we represent it in /sys/module and create the
linkages.

I created some horrible patches to try to track this down, as it was
reported on lkml (look for "Subject: kref refcounting breakage in mainline" )
but never got it working correctly.

I bet if you build that code as a module, it will work just fine, can
you try it?

Kay, did you ever get a chance to look into this reference counting
issue?

thanks,

greg k-h
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