Date: Tue, 28 Mar 2006 13:58:24 -0500 From: John Baldwin <jhb@freebsd.org> To: "Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?=" <des@des.no> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/i386/include atomic.h Message-ID: <200603281358.26703.jhb@freebsd.org> In-Reply-To: <86psk6wilj.fsf@xps.des.no> References: <200603281434.k2SEYmaR031447@repoman.freebsd.org> <200603281300.09419.jhb@freebsd.org> <86psk6wilj.fsf@xps.des.no>
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On Tuesday 28 March 2006 13:05, Dag-Erling Sm=F8rgrav wrote:
> John Baldwin <jhb@freebsd.org> writes:
> > One reason for not having the casts, btw, is that you lose type
> > checking.
>=20
> Huh? Before my patch, any use of atomic_*_ptr with warnings turned
> off would result in a slew of warnings because you'd be passing
> pointers to a function which is declared to take u_int. The only way
> to make this type safe is to use inline functions instead of the
> macros I wrote.
s/off/on/ I trust
Not true. The tinderbox would attest to that. Please see code such as
this:
#define MTX_UNOWNED 0x00000004 /* Cookie for free mutex */
=2E..
/* Try to obtain mtx_lock once. */
#ifndef _obtain_lock
#define _obtain_lock(mp, tid) \
atomic_cmpset_acq_ptr(&(mp)->mtx_lock, MTX_UNOWNED, (tid))
#endif
=2E..
void
_mtx_lock_sleep(struct mtx *m, uintptr_t tid, int opts, const char *file,
int line)
{
...
uintptr_t v;
...
while (!_obtain_lock(m, tid)) {
...
v =3D m->mtx_lock;
...
/*
* If the mutex isn't already contested and a failure occurs
* setting the contested bit, the mutex was either released
* or the state of the MTX_RECURSED bit changed.
*/
if ((v & MTX_CONTESTED) =3D=3D 0 &&
!atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) {
...
continue;
}
...
}
...
}
etc. kern_rwlock.c has this as well. The parts of the kernel that
do use pointers already use explicit casts to uintptr_t where needed:
dev/hatm/if_hatm_intr.c: if (atomic_cmpset_ptr((uintptr_t *)=
list, (uintptr_t)buf->link,
dev/hatm/if_hatm_intr.c: if (atomic_cmpset_ptr((uintptr_t *)=
&sc->mbuf_list[g],
dev/hatm/if_hatm_intr.c: if (atomic_cmpset_ptr((uint=
ptr_t *)&sc->mbuf_list[g],
Even userland uses casts when it uses void * rather than uintptr_t for
the underlying type. See src/lib/libpthread/sys/lock.c or
src/lib/libthr/thr_umtx.h.
=2D-=20
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" =3D http://www.FreeBSD.org
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