Re: [RFC] I/O MCA recovery

[Russ Anderson <rja@sgi.com>]

Jesse Barnes wrote:
> On Thursday, May 13, 2004 2:02 am, Luck, Tony wrote:
> > >There are also locking problems, since at the moment an MCA
> > >could occur on multiple processors, but I think the MCA code
> > >in general doesn't handle that case...
> >
> > At the moment the MCA code serializes simulaneous MCA on multiple
> > processors (see the hand-crafted spinlock in mca_asm.S at the
> > ia64_os_mca_spin label).
> 
> Thanks Tony, I hadn't looked at that code in awhile.  I guess the I/O error 
> recovery code should try to acquire the io_range_list_lock before looking 
> through the list.  If it can't get the lock, we just have to give up and make 
> the error unrecoverable since we don't know if another CPU will take an MCA 
> while holding that lock, leaving the list in a bad state...

Seems like spinning on a trylock for a short period would
be reasonable.  It everything is OK, the process with the
lock will let go quickly.  Otherwise, we're probably dead
anyway.
 
> I don't *think* that doing unconditional rendezvous in the PROM will help this 
> situation either, but maybe someone else has good ideas about how to handle 
> that?

In general, I suggest avoiding rendezvous unless there is a really
obvious reason to do so.  In this case, I think you're right.

-- 
Russ Anderson, OS RAS/Partitioning Project Lead  
SGI - Silicon Graphics Inc          rja@sgi.com