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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