On Fri, 16 Sep 2016 11:43:13 +0000 David Laight <david.lai...@aculab.com> wrote:
> From: Nicholas Piggin > > Sent: 16 September 2016 10:53 > > On Thu, 15 Sep 2016 18:31:54 +0530 > > Madhavan Srinivasan <ma...@linux.vnet.ibm.com> wrote: > > > > > Force use of soft_enabled_set() wrapper to update paca-soft_enabled > > > wherever possisble. Also add a new wrapper function, > > > soft_enabled_set_return(), > > > added to force the paca->soft_enabled updates. > ... > > > diff --git a/arch/powerpc/include/asm/hw_irq.h > > > b/arch/powerpc/include/asm/hw_irq.h > > > index 8fad8c24760b..f828b8f8df02 100644 > > > --- a/arch/powerpc/include/asm/hw_irq.h > > > +++ b/arch/powerpc/include/asm/hw_irq.h > > > @@ -53,6 +53,20 @@ static inline notrace void soft_enabled_set(unsigned > > > long enable) > > > : : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled))); > > > } > > > > > > +static inline notrace unsigned long soft_enabled_set_return(unsigned > > > long enable) > > > +{ > > > + unsigned long flags; > > > + > > > + asm volatile( > > > + "lbz %0,%1(13); stb %2,%1(13)" > > > + : "=r" (flags) > > > + : "i" (offsetof(struct paca_struct, soft_enabled)),\ > > > + "r" (enable) > > > + : "memory"); > > > + > > > + return flags; > > > +} > > > > Why do you have the "memory" clobber here while soft_enabled_set() does > > not? > > I wondered about the missing memory clobber earlier. > > Any 'clobber' ought to be restricted to the referenced memory area. > If the structure is only referenced by r13 through 'asm volatile' it isn't > needed. Well a clobber (compiler barrier) at some point is needed in irq_disable and irq_enable paths, so we correctly open and close the critical section vs interrupts. I just wonder about these helpers. It might be better to take the clobbers out of there and add barrier(); in callers, which would make it more obvious.