On Wed, Jun 01, 2016 at 11:11:38AM +0800, Boqun Feng wrote:
> Hi Peter,
>
> On Tue, May 31, 2016 at 12:19:44PM +0200, Peter Zijlstra wrote:
> [snip]
> >
> > @@ -329,20 +361,53 @@ atomic64_##op##_return_relaxed(long a, a
> > return t; \
> > }
> >
> > +#define ATOMIC64_FETCH_OP_RELAXED(op, asm_op)
> > \
> > +static inline long \
> > +atomic64_fetch_##op##_relaxed(long a, atomic64_t *v)
> > \
> > +{ \
> > + long res, t; \
> > + \
> > + __asm__ __volatile__( \
> > +"1: ldarx %0,0,%4 # atomic64_fetch_" #op "_relaxed\n"
> > \
> > + #asm_op " %1,%3,%0\n" \
> > +" stdcx. %1,0,%4\n" \
> > +" bne- 1b\n" \
> > + : "=&r" (res), "=&r" (t), "+m" (v->counter) \
> > + : "r" (a), "r" (&v->counter) \
> > + : "cc"); \
> > + \
> > + return t; \
>
> Looks like I missed this one in v1, it should be
>
> return res;
>
> because the primitives will return the values before modified by the
> operations.
> FWIW, I tested on ppc with ATOMIC64_SELFTEST=y for the following branch: git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/atomic (afee54ef5b1f2b04) without this modification, I can hit: ------------[ cut here ]------------ kernel BUG at lib/atomic64_test.c:181! Oops: Exception in kernel mode, sig: 5 [#1] with this modification, all the atomic selftests are passed ;-) Regards, Boqun
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