On 19/02/18(Mon) 16:31, Mark Kettenis wrote:
> > Date: Mon, 19 Feb 2018 16:22:30 +0100
> > From: Martin Pieuchot <[email protected]>
> >
> > Now that suser() is no longer messing with a per-process field, we
> > can directly turn setrtable(2) as NOLOCK.
> >
> > Apart from sanity checks this syscall writes an int-sized per-process
> > field. Is a memory barrier enough?
> >
> > ok?
>
> I'm wondering if we need a memory barrier here at all. What race are
> you trying to prevent here?
I just wanted to be sure the change is visible to other threads of the
same process when the current one is finished. Syscalls that grab the
KERNEL_LOCK() or a rwlock have an implicit barrier when they release
their lock. So I was wondering if I needed to add one here. But I'd
be glade to hear if this is not needed and why :)
> > Index: kern/syscalls.master
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/syscalls.master,v
> > retrieving revision 1.180
> > diff -u -p -r1.180 syscalls.master
> > --- kern/syscalls.master 12 Dec 2017 01:12:34 -0000 1.180
> > +++ kern/syscalls.master 19 Feb 2018 15:05:34 -0000
> > @@ -532,7 +532,7 @@
> > 307 OBSOL statfs53
> > 308 OBSOL fstatfs53
> > 309 OBSOL fhstatfs53
> > -310 STD { int sys_setrtable(int rtableid); }
> > +310 STD NOLOCK { int sys_setrtable(int rtableid); }
> > 311 STD NOLOCK { int sys_getrtable(void); }
> > 312 OBSOL t32_getdirentries
> > 313 STD { int sys_faccessat(int fd, const char *path, \
> > Index: kern/uipc_syscalls.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/uipc_syscalls.c,v
> > retrieving revision 1.165
> > diff -u -p -r1.165 uipc_syscalls.c
> > --- kern/uipc_syscalls.c 19 Feb 2018 08:59:52 -0000 1.165
> > +++ kern/uipc_syscalls.c 19 Feb 2018 15:19:35 -0000
> > @@ -1189,6 +1190,9 @@ sys_setrtable(struct proc *p, void *v, r
> > return (EINVAL);
> >
> > p->p_p->ps_rtableid = (u_int)rtableid;
> > + /* Force visibility */
> > + membar_producer();
> > +
> > return (0);
> > }
> >
> >
> >
>
