Re: call_usermodehelper hang

[Greg KH <greg@kroah.com>]

On Tue, Apr 06, 2004 at 05:29:03PM -0700, Andrew Morton wrote:
> Brian King <brking@us.ibm.com> wrote:
> >
> > I have been running into some kernel hangs due to call_usermodehelper. Looking
> > at the backtrace, it looks to me like there are deadlock issues with adding
> > devices from work queues. Attached is a sample backtrace from one of the
> > hangs I experienced. My question is why does call_usermodehelper do 2 different
> > things depending on whether or not it is called from the kevent task? It appears
> > that the simple way to fix the hang would be to never have call_usermodehelper
> > use a work_queue since it must be called from process context anyway, or
> > am I missing something?
> > 
> 
> swapper is running call_usermodehelper() while holding
> down_write(&bus->subsys.rwsem); via bus_add_driver().
> 
> Meanwhile, keventd is blocked on the same lock in bus_add_device().
> 
> I'd say that the bug lies in the kobject code - we should not call
> call_usermodehelper() while holding any locks which keventd may ever
> acquire.

How is keventd calling sysfs code?  Is scsi using it to drive device
detection somehow?  I don't see how the kobject core code itself can do
this on its own.

thanks,

greg k-h