On Fri, Jul 18, 2014 at 12:28 PM, Mikael Pettersson
<mikpeli...@gmail.com> wrote:
> John David Anglin writes:
> > Because the atomic sync functions in config/pa/linux-atomic.c are not
> > lock free, we need to use
> > __kernel_cmpxchg for the __sync_lock_release. This was found in
> > glibc's pthread_spin_unlock
> > implementation.
> >
> > Tested on hppa-unknown-linux-gnu. Committed to trunk.
>
> It seems to me that ARM's linux-atomic.c has the same problem.
> CC:ing some ARM folks for clarification.
Prima-facie I'm worried about the 8 byte store case as that's not
guaranteed atomic on all MP implementations (you need LPAE IIRC to
guarantee this).
All other cases look sane to me as the 1,2, 4 byte accesses should be atomic.
Ramana
>
> /Mikael
>
> >
> > Dave
> > --
> > John David Anglin dave.ang...@bell.net
> >
> >
> >
> >
> > ----------------------------------------------------------------------
> > 2014-07-17 John David Anglin <dang...@gcc.gnu.org>
> >
> > * config/pa/linux-atomic.c (__sync_lock_release_4): New.
> > (SYNC_LOCK_RELEASE): Update to use __kernel_cmpxchg for release.
> > Don't use SYNC_LOCK_RELEASE for int type.
> >
> > Index: config/pa/linux-atomic.c
> > ===================================================================
> > --- config/pa/linux-atomic.c (revision 210671)
> > +++ config/pa/linux-atomic.c (working copy)
> > @@ -293,13 +293,34 @@
> > SUBWORD_TEST_AND_SET (unsigned short, 2)
> > SUBWORD_TEST_AND_SET (unsigned char, 1)
> >
> > +void HIDDEN
> > +__sync_lock_release_4 (int *ptr)
> > +{
> > + int failure, oldval;
> > +
> > + do {
> > + oldval = *ptr;
> > + failure = __kernel_cmpxchg (oldval, 0, ptr);
> > + } while (failure != 0);
> > +}
> > +
> > #define SYNC_LOCK_RELEASE(TYPE, WIDTH)
> \
> > void HIDDEN
> \
> > __sync_lock_release_##WIDTH (TYPE *ptr) \
> > { \
> > - *ptr = 0;
> \
> > + int failure; \
> > + unsigned int oldval, newval, shift, mask;
> \
> > + int *wordptr = (int *) ((unsigned long) ptr & ~3);
> \
> > + \
> > + shift = (((unsigned long) ptr & 3) << 3) ^ INVERT_MASK_##WIDTH; \
> > + mask = MASK_##WIDTH << shift; \
> > + \
> > + do { \
> > + oldval = *wordptr; \
> > + newval = oldval & ~mask;
> \
> > + failure = __kernel_cmpxchg (oldval, newval, wordptr); \
> > + } while (failure != 0); \
> > }
> >
> > -SYNC_LOCK_RELEASE (int, 4)
> > SYNC_LOCK_RELEASE (short, 2)
> > SYNC_LOCK_RELEASE (char, 1)
>
> --
