linux-kernel - Re: kobject: delayed kobject release: help find buggy drivers

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Date:	Thu, 5 Sep 2013 08:34:57 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Dave Jones <davej@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	rmk+kernel@....linux.org.uk
Subject: Re: kobject: delayed kobject release: help find buggy drivers

On Thu, Sep 05, 2013 at 01:19:45AM -0400, Dave Jones wrote:
> On Wed, Sep 04, 2013 at 09:57:45PM -0700, Greg KH wrote:
>  > On Thu, Sep 05, 2013 at 12:13:38AM -0400, Dave Jones wrote:
>  > > On Wed, Sep 04, 2013 at 02:53:11PM +0930, Rusty Russell wrote:
>  > >  
>  > >  > >> With this enabled, I get a bunch of scrolling oopses immediately after
>  > >  > >> exiting the bootloader. It happens so early I can't even capture them
>  > >  > >> over usb-serial, or earlyprintk=dbgp.
>  > >  > >> 
>  > >  > >> And for whatever reason, the printk path while oopsing ignores boot_delay parameter,
>  > >  > >> so I can't even use that.
>  > >  > >> 
>  > >  > >> any ideas ?
>  > >  > >
>  > >  > > The first big bug found with this was with the module kobject code, and
>  > >  > > a fix for that should be going in through Rusty's tree to Linus for this
>  > >  > > merge window (right Rusty?)
>  > >  > 
>  > >  > Yep, just sent pull request.  The fix was the final commit there...
>  > > 
>  > > Crap, that isn't the bug I'm hitting.
>  > 
>  > Any chance to get a oops traceback?
> 
> Got it. (I think I was getting tracebacks from multiple cpus, hence the spewing).
> Adding a check for tainted() = infinite loop to show_backtrace() combined with boot_delay
> gave me a really long oops that I had to grab video to record.

Odd, but thanks for going through all of that.

> RIP: <null>
> 
> Trace:
> <IRQ>
> run_timer_softirq
> __do_softirq
> irq_exit
> smp_apic_timer_interrupt
> apic_timer_interrupt
> <EOI>
> vprintk_emit
> dev_vprintk_emit
> dev_vprint_emit
> __dev_printk
> _dev_info
> ahci_print_info
> ahci_init_one
> local_pci_probe
> pci_device_probe
> driver_probe_device
> __driver_attach
> bus_for_each_dev
> driver_attach
> bus_add_driver
> driver_register
> __pci_register_driver
> ahci_pci_driver_init

So we are loading a ahci driver here.  Any hint as to which
driver/device this is?  Is it a device that fails for this driver, and
then falls back to another more "specific" one?

And dieing in ahci_print_info()?  That's very strange.

Russell (not Rusty), any thoughts about this one?  You've been able to
debug a bunch of these tracebacks recently really well.

thanks,

greg k-h
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