Subject: Re: next-20090310: ext4 hangs

From: Jan Kara <[email-masked]>
Date: Thu, 26 Mar 2009 01:25:55 +0100

On Thu 26-03-09 01:17:06, Jiri Gaisler wrote:
> Jan Kara wrote:
> >   Hi,
> > 
> >   thanks for the updated disassembly.
> > 
> >>   55bab0:       82 10 60 01     or  %g1, 1, %g1
> >>                 spin_unlock(&journal->j_list_lock);
> >>   55bab4:       40 06 4b 20     call  6ee734 <_spin_unlock>
> >>   55bab8:       c2 24 e0 28     st  %g1, [ %l3 + 0x28 ]
> >   OK, so it really seems that:
> >   jinode->i_flags |= JI_COMMIT_RUNNING;
> >   spin_unlock(&journal->j_list_lock);
> > 
> >   has been compiled to
> >   ld [ %l3 + 0x28 ], %g1
> >   or  %g1, 1, %g1
> >   call  6ee734 <_spin_unlock>
> >   st  %g1, [ %l3 + 0x28 ]
> > 
> >   Which seems like a bug in the compiler or in the way implement compiler
> > barriers in spin_unlock() on UP sparc. Or is there some sparc magic by which
> > this is correct code? Any clever sparc guy?
> > 
> Looks fine to me - the store is made in the branch delay slot
> of the call, so it will occur before the first instruction at
> the call target address executes.
  Thanks for explanation. I knew sparc had some surprising features like
this ;).
								Honza
-- 
Jan Kara <[email-masked]>
SUSE Labs, CR