Re: [Xen-devel] [PATCH v3 01/41] lcoking/barriers, arch: Use smp barriers in smp_store_release()

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Tue, Jan 12, 2016 at 08:28:44AM -0800, Paul E. McKenney wrote:
> On Sun, Jan 10, 2016 at 04:16:32PM +0200, Michael S. Tsirkin wrote:
> > From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> > 
> > With commit b92b8b35a2e ("locking/arch: Rename set_mb() to smp_store_mb()")
> > it was made clear that the context of this call (and thus set_mb)
> > is strictly for CPU ordering, as opposed to IO. As such all archs
> > should use the smp variant of mb(), respecting the semantics and
> > saving a mandatory barrier on UP.
> > 
> > Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Cc: <linux-arch@xxxxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Tony Luck <tony.luck@xxxxxxxxx>
> > Cc: dave@xxxxxxxxxxxx
> > Link: 
> > http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave@xxxxxxxxxxxx
> > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> 
> Aside from a need for s/lcoking/locking/ in the subject line:
> 
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Thanks!
Though Ingo already put this in tip tree like this,
and I need a copy in my tree to avoid breaking bisect,
so I will probably keep it exactly the same to avoid confusion.

> > ---
> >  arch/ia64/include/asm/barrier.h    | 2 +-
> >  arch/powerpc/include/asm/barrier.h | 2 +-
> >  arch/s390/include/asm/barrier.h    | 2 +-
> >  include/asm-generic/barrier.h      | 2 +-
> >  4 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/ia64/include/asm/barrier.h 
> > b/arch/ia64/include/asm/barrier.h
> > index df896a1..209c4b8 100644
> > --- a/arch/ia64/include/asm/barrier.h
> > +++ b/arch/ia64/include/asm/barrier.h
> > @@ -77,7 +77,7 @@ do {                                                      
> >                 \
> >     ___p1;                                                          \
> >  })
> > 
> > -#define smp_store_mb(var, value)   do { WRITE_ONCE(var, value); mb(); } 
> > while (0)
> > +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } 
> > while (0)
> > 
> >  /*
> >   * The group barrier in front of the rsm & ssm are necessary to ensure
> > diff --git a/arch/powerpc/include/asm/barrier.h 
> > b/arch/powerpc/include/asm/barrier.h
> > index 0eca6ef..a7af5fb 100644
> > --- a/arch/powerpc/include/asm/barrier.h
> > +++ b/arch/powerpc/include/asm/barrier.h
> > @@ -34,7 +34,7 @@
> >  #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
> >  #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
> > 
> > -#define smp_store_mb(var, value)   do { WRITE_ONCE(var, value); mb(); } 
> > while (0)
> > +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } 
> > while (0)
> > 
> >  #ifdef __SUBARCH_HAS_LWSYNC
> >  #    define SMPWMB      LWSYNC
> > diff --git a/arch/s390/include/asm/barrier.h 
> > b/arch/s390/include/asm/barrier.h
> > index d68e11e..7ffd0b1 100644
> > --- a/arch/s390/include/asm/barrier.h
> > +++ b/arch/s390/include/asm/barrier.h
> > @@ -36,7 +36,7 @@
> >  #define smp_mb__before_atomic()            smp_mb()
> >  #define smp_mb__after_atomic()             smp_mb()
> > 
> > -#define smp_store_mb(var, value)           do { WRITE_ONCE(var, value); 
> > mb(); } while (0)
> > +#define smp_store_mb(var, value)   do { WRITE_ONCE(var, value); smp_mb(); 
> > } while (0)
> > 
> >  #define smp_store_release(p, v)                                            
> > \
> >  do {                                                                       
> > \
> > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> > index b42afad..0f45f93 100644
> > --- a/include/asm-generic/barrier.h
> > +++ b/include/asm-generic/barrier.h
> > @@ -93,7 +93,7 @@
> >  #endif     /* CONFIG_SMP */
> > 
> >  #ifndef smp_store_mb
> > -#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } 
> > while (0)
> > +#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); } 
> > while (0)
> >  #endif
> > 
> >  #ifndef smp_mb__before_atomic
> > -- 
> > MST
> > 

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