On Wed, Jun 6, 2018 at 8:57 AM, Justin Hibbits <jhibb...@freebsd.org> wrote:
> Author: jhibbits > Date: Wed Jun 6 12:57:11 2018 > New Revision: 334708 > URL: https://svnweb.freebsd.org/changeset/base/334708 > > Log: > Add a memory barrier after taking a reference on the vnode holdcnt in > _vhold > > This is needed to avoid a race between the VNASSERT() below, and another > thread updating the VI_FREE flag, on weakly-ordered architectures. > > On a 72-thread POWER9, without this barrier a 'make -j72 buildworld' > would > panic on the assert regularly. > > It may be possible to use a weaker barrier, and I'll investigate that > once > all stability issues are worked out on POWER9. > > Modified: > head/sys/kern/vfs_subr.c > > Modified: head/sys/kern/vfs_subr.c > ============================================================ > ================== > --- head/sys/kern/vfs_subr.c Wed Jun 6 10:46:24 2018 (r334707) > +++ head/sys/kern/vfs_subr.c Wed Jun 6 12:57:11 2018 (r334708) > @@ -2807,6 +2807,9 @@ _vhold(struct vnode *vp, bool locked) > CTR2(KTR_VFS, "%s: vp %p", __func__, vp); > if (!locked) { > if (refcount_acquire_if_not_zero(&vp->v_holdcnt)) { > +#if !defined(__amd64__) && !defined(__i386__) > + mb(); > +#endif > VNASSERT((vp->v_iflag & VI_FREE) == 0, vp, > ("_vhold: vnode with holdcnt is free")); > return; > > So why isn't the refcount_acquire() enough? Warner _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
