Re: [RFC PATCH V2 FIX] Fix deadlock during find

[Michael Trimarchi <trimarchimichael@yahoo.it>]

Hi,

--- Sab 6/12/08, Paul Mundt <lethal@linux-sh.org> ha scritto:

> Da: Paul Mundt <lethal@linux-sh.org>
> Oggetto: Re: [RFC PATCH V2 FIX] Fix deadlock during find
> A: "Michael Trimarchi" <trimarchimichael@yahoo.it>
> Cc: linux-sh@vger.kernel.org
> Data: Sabato 6 dicembre 2008, 14:01
> On Wed, Nov 26, 2008 at 01:04:28PM +0000, Michael Trimarchi
> wrote:
> > ----- Messaggio originale -----
> > > Da: Paul Mundt <lethal@linux-sh.org>
> > > A: Michael Trimarchi
> <trimarchimichael@yahoo.it>
> > > Cc: linux-sh@vger.kernel.org
> > > Inviato: Marted? 25 novembre 2008, 18:06:03
> > > Oggetto: Re: [RFC PATCH V2 FIX] Fix deadlock
> during find
> > > 
> [snip]
> 
> > > > @@ -48,18 +48,18 @@
> __mutex_fastpath_lock_retval(atomic_t *count, int 
> > > (*fail_fn)(atomic_t *))
> > > >  static inline void
> > > >  __mutex_fastpath_unlock(atomic_t *count,
> void (*fail_fn)(atomic_t *))
> > > >  {
> > > > -    int __res, __orig;
> > > > +    int __res;
> > > >  
> > > >      __asm__ __volatile__ (
> > > > -        "movli.l    @%2, %0   
> \n\t"
> > > > -        "mov        %0, %1   
> \n\t"
> > > > +        "1: movli.l    @%1, %0   
> \n\t"
> > > >          "add        #1, %0   
> \n\t"
> > > > -        "movco.l    %0, @%2 "
> > > > -        : "=&z" (__res),
> "=&r" (__orig)
> > > > +        "movco.l    %0, @%1
> \n\t"
> > > > +        "bf       
> 1b\n\t"
> > > > +        : "=&z" (__res)
> > > >          : "r"
> (&(count)->counter)
> > > >          : "t" );
> > > >  
> > > > -    if (unlikely(__orig != 0))
> > > > +    if (unlikely(__res <= 0))
> > > >          fail_fn(count);
> > > >  }
> > > >  
> > > 
> > > Making __mutex_fastpath_unlock() loop seems
> counter-intuitive. I think
> > > the initial test on __orig is what was causing
> you issues rather than the
> > > need for looping. I do see why ARM did it this
> way, but we don't have
> > > precisely the same semantics there.
> > > 
> > > Does the following patch against current git pass
> your test cases?
> > > 
> >  This is an old one patch. You integrate the correct
> one V3
> > 
> The patch in question was against what is in current git.
> The very
> definition of the fast-path is that it is a single-shot
> that isn't busy
> looping, as that is what the slow path does. Unless you see
> any
> particular issues with my patch, I will queue it up, as it
> brings us back
> in line with what the fast-path semantics are supposed to
> be. So far I
> haven't had any issues with the refactored fast-path.

I'm agree with you.

Regards Michael