Re: [linux-usb-devel] Re: 2.6.14-rc1 load average calculation broken?

[Mike Anderson <andmike@us.ibm.com>]

Alan Stern <stern@rowland.harvard.edu> wrote:
> On Sat, 17 Sep 2005, Jan Dittmer wrote:
> 
> > > Maybe the wakeup occurred before ap->ops was set correctly, or after it 
> > > was unset.  Jan, at what point did the oops happen?  Was it right after 
> > > the device was detected, during removal, or some other time?
> > > 
> > > Can you put in some debugging printk's to see what values are in ap, 
> > > ap->ops, and ap->ops->eng_timeout?
> > 
> > ap->ops is 0, on dereferencing I get a backtrace. ap has a valid pointer
> > (-573296044 whatever that maps to).
> 
> Hmm...  I imagine that when the error handler is first starting up,
> ->host_busy is equal to ->host_failed because both are 0.  So that really
> is not the appropriate condition to wait for.  A better approach would be
> to have an atomic_t variable recording the number of pending invocations.
> 
> On the whole, I wonder if using kthread_stop here is such a good idea.  
> The old mechanism for stopping worked well...
> 

Since scsi_eh_wakeup can only be called on a completion or timeout of an IO
you cannot get a comparison when both are 0 (unless we have a bug
somewhere).

If the increment of host_failed, increment of host_busy, decrement of
host_busy, and the comparison of host_busy to host_failed is all under
the host_lock why would the atomic_t be better.

-andmike
--
Michael Anderson
andmike@us.ibm.com