On Fri, Sep 18, 2015 at 12:22:52PM +0100, Peter Zijlstra wrote: > On Fri, Sep 18, 2015 at 10:28:20AM +0100, Will Deacon wrote: > > On Fri, Sep 18, 2015 at 10:06:46AM +0100, Dmitry Vyukov wrote: > > > > Can we have something along the lines of: > > > > > > #define atomic_read_ctrl(v) READ_ONCE_CTRL(&(v)->counter) > > > > Funnily enough, I had this exact same discussion off-list yesterday > > afternoon, since I wrote some code relying on a ctrl dependency from > > an atomic_read to an atomic_xchg_relaxed. > > Something a little like so should work fine I suppose. > > --- > Subject: atomic: Implement atomic_read_ctrl() > > Provide atomic_read_ctrl() to mirror READ_ONCE_CTRL(), such that we can > more conveniently use atomics in control dependencies. > > Since we can assume atomic_read() implies a READ_ONCE(), we must only > emit an extra smp_read_barrier_depends() in order to upgrade to > READ_ONCE_CTRL() semantics. > > Requested-by: Dmitry Vyukov <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > --- > include/linux/atomic.h | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/include/linux/atomic.h b/include/linux/atomic.h > index 00a5763e850e..c4072421ea7f 100644 > --- a/include/linux/atomic.h > +++ b/include/linux/atomic.h > @@ -4,6 +4,15 @@ > #include <asm/atomic.h> > #include <asm/barrier.h> > > +#ifndef atomic_read_ctrl > +static inline int atomic_read_ctrl(atomic_t *v) > +{ > + int val = atomic_read(v); > + smp_read_barrier_depends(); /* Enforce control dependency. */ > + return val; > +} > +#endif > + > /* > * Relaxed variants of xchg, cmpxchg and some atomic operations. > *
Works for me: Acked-by: Will Deacon <[email protected]> Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
