Date: Wed, 5 Sep 2018 01:24:13 +0000 (UTC) From: Mark Johnston <markj@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org Subject: svn commit: r338463 - stable/11/sys/kern Message-ID: <201809050124.w851ODb8061899@repo.freebsd.org>
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Author: markj Date: Wed Sep 5 01:24:13 2018 New Revision: 338463 URL: https://svnweb.freebsd.org/changeset/base/338463 Log: MFC r337974: Add INVARIANTS-only fences around lockless vnode refcount updates. Modified: stable/11/sys/kern/vfs_subr.c Directory Properties: stable/11/ (props changed) Modified: stable/11/sys/kern/vfs_subr.c ============================================================================== --- stable/11/sys/kern/vfs_subr.c Wed Sep 5 00:30:34 2018 (r338462) +++ stable/11/sys/kern/vfs_subr.c Wed Sep 5 01:24:13 2018 (r338463) @@ -116,6 +116,22 @@ static void vfs_knl_assert_unlocked(void *arg); static void destroy_vpollinfo(struct vpollinfo *vi); /* + * These fences are intended for cases where some synchronization is + * needed between access of v_iflags and lockless vnode refcount (v_holdcnt + * and v_usecount) updates. Access to v_iflags is generally synchronized + * by the interlock, but we have some internal assertions that check vnode + * flags * without acquiring the lock. Thus, these fences are INVARIANTS-only + * for now. + */ +#ifdef INVARIANTS +#define VNODE_REFCOUNT_FENCE_ACQ() atomic_thread_fence_acq() +#define VNODE_REFCOUNT_FENCE_REL() atomic_thread_fence_rel() +#else +#define VNODE_REFCOUNT_FENCE_ACQ() +#define VNODE_REFCOUNT_FENCE_REL() +#endif + +/* * Number of vnodes in existence. Increased whenever getnewvnode() * allocates a new vnode, decreased in vdropl() for VI_DOOMED vnode. */ @@ -1006,6 +1022,7 @@ vnlru_free_locked(int count, struct vfsops *mnt_op) */ freevnodes--; vp->v_iflag &= ~VI_FREE; + VNODE_REFCOUNT_FENCE_REL(); refcount_acquire(&vp->v_holdcnt); mtx_unlock(&vnode_free_list_mtx); @@ -2429,6 +2446,7 @@ v_incr_usecount(struct vnode *vp) if (vp->v_type != VCHR && refcount_acquire_if_not_zero(&vp->v_usecount)) { + VNODE_REFCOUNT_FENCE_ACQ(); VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp, ("vnode with usecount and VI_OWEINACT set")); } else { @@ -2527,6 +2545,7 @@ vget(struct vnode *vp, int flags, struct thread *td) } else { oweinact = 1; vp->v_iflag &= ~VI_OWEINACT; + VNODE_REFCOUNT_FENCE_REL(); } refcount_acquire(&vp->v_usecount); v_incr_devcount(vp); @@ -2740,6 +2759,7 @@ _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)) { + VNODE_REFCOUNT_FENCE_ACQ(); VNASSERT((vp->v_iflag & VI_FREE) == 0, vp, ("_vhold: vnode with holdcnt is free")); return;
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