mirror of https://github.com/NetBSD/src.git
Add a marker VUSECOUNT_VGET to v_usecount that gets set whenever
vcache_vget() or vache_tryvget() succeeds. Use it to rerun VOP_INACTIVE() if another thread ran a vget()..vrele() cycle while we inactivated our last reference.bouyer-sunxi-drm
hannken
parent
5d699a7a71
commit
9c423f2391
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@ -1,4 +1,4 @@
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/* $NetBSD: vfs_vnode.c,v 1.131 2022/02/17 14:38:06 hannken Exp $ */
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/* $NetBSD: vfs_vnode.c,v 1.132 2022/02/17 14:39:14 hannken Exp $ */
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/*-
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* Copyright (c) 1997-2011, 2019, 2020 The NetBSD Foundation, Inc.
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@ -148,7 +148,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.131 2022/02/17 14:38:06 hannken Exp $");
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__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.132 2022/02/17 14:39:14 hannken Exp $");
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#ifdef _KERNEL_OPT
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#include "opt_pax.h"
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@ -232,9 +232,12 @@ extern struct vfsops dead_vfsops;
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/*
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* The high bit of v_usecount is a gate for vcache_tryvget(). It's set
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* only when the vnode state is LOADED.
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* The next bit of v_usecount is a flag for vrelel(). It's set
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* from vcache_vget() and vcache_tryvget() whenever the operation succeeds.
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*/
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#define VUSECOUNT_MASK 0x7fffffff
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#define VUSECOUNT_MASK 0x3fffffff
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#define VUSECOUNT_GATE 0x80000000
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#define VUSECOUNT_VGET 0x40000000
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/*
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* Return the current usecount of a vnode.
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@ -777,8 +780,10 @@ vrelel(vnode_t *vp, int flags, int lktype)
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{
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const bool async = ((flags & VRELEL_ASYNC) != 0);
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bool recycle, defer;
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u_int use, next;
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int error;
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retry:
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KASSERT(mutex_owned(vp->v_interlock));
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if (__predict_false(vp->v_op == dead_vnodeop_p &&
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@ -787,17 +792,34 @@ vrelel(vnode_t *vp, int flags, int lktype)
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}
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/*
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* If not the last reference, just drop the reference count and
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* unlock. VOP_UNLOCK() is called here without a vnode reference
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* held, but is ok as the hold of v_interlock will stop the vnode
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* from disappearing.
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* If not the last reference, just unlock and drop the reference count.
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*
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* Otherwise make sure we pass a point in time where we hold the
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* last reference with VGET flag unset.
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*/
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if (vtryrele(vp)) {
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if (lktype != LK_NONE) {
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VOP_UNLOCK(vp);
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for (use = atomic_load_relaxed(&vp->v_usecount);; use = next) {
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if (__predict_false((use & VUSECOUNT_MASK) > 1)) {
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if (lktype != LK_NONE) {
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mutex_exit(vp->v_interlock);
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lktype = LK_NONE;
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VOP_UNLOCK(vp);
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mutex_enter(vp->v_interlock);
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}
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if (vtryrele(vp)) {
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mutex_exit(vp->v_interlock);
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return;
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}
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next = atomic_load_relaxed(&vp->v_usecount);
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continue;
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}
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KASSERT((use & VUSECOUNT_MASK) == 1);
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next = use & ~VUSECOUNT_VGET;
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if (next != use) {
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next = atomic_cas_uint(&vp->v_usecount, use, next);
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}
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if (__predict_true(next == use)) {
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break;
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}
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mutex_exit(vp->v_interlock);
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return;
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}
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if (vrefcnt(vp) <= 0 || vp->v_writecount != 0) {
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vnpanic(vp, "%s: bad ref count", __func__);
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@ -879,32 +901,20 @@ vrelel(vnode_t *vp, int flags, int lktype)
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rw_enter(vp->v_uobj.vmobjlock, RW_WRITER);
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mutex_enter(vp->v_interlock);
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for (;;) {
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/*
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* If no longer the last reference, try to shed it.
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* On success, drop the interlock last thereby
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* preventing the vnode being freed behind us.
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*/
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if (vtryrele(vp)) {
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VOP_UNLOCK(vp);
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rw_exit(vp->v_uobj.vmobjlock);
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mutex_exit(vp->v_interlock);
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return;
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/*
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* Block new references then check again to see if a
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* new reference was acquired in the meantime. If
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* it was, restore the vnode state and try again.
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*/
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if (recycle) {
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VSTATE_CHANGE(vp, VS_LOADED, VS_BLOCKED);
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use = atomic_load_relaxed(&vp->v_usecount);
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if ((use & VUSECOUNT_VGET) != 0 ||
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(use & VUSECOUNT_MASK) != 1) {
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VSTATE_CHANGE(vp, VS_BLOCKED, VS_LOADED);
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goto retry;
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}
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/*
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* Block new references then check again to see if a
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* new reference was acquired in the meantime. If
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* it was, restore the vnode state and try again.
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*/
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if (recycle) {
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VSTATE_CHANGE(vp, VS_LOADED, VS_BLOCKED);
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if (vrefcnt(vp) != 1) {
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VSTATE_CHANGE(vp, VS_BLOCKED, VS_LOADED);
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continue;
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}
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}
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break;
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}
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}
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/* Take care of space accounting. */
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if ((vp->v_iflag & VI_EXECMAP) != 0) {
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@ -921,17 +931,30 @@ vrelel(vnode_t *vp, int flags, int lktype)
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if (recycle) {
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VSTATE_ASSERT(vp, VS_BLOCKED);
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/* vcache_reclaim drops the lock. */
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lktype = LK_NONE;
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vcache_reclaim(vp);
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} else {
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lktype = LK_NONE;
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VOP_UNLOCK(vp);
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}
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KASSERT(vrefcnt(vp) > 0);
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out:
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if ((atomic_dec_uint_nv(&vp->v_usecount) & VUSECOUNT_MASK) != 0) {
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/* Gained another reference while being reclaimed. */
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mutex_exit(vp->v_interlock);
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return;
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for (use = atomic_load_relaxed(&vp->v_usecount);; use = next) {
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if (__predict_false((use & VUSECOUNT_VGET) != 0 &&
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(use & VUSECOUNT_MASK) == 1)) {
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/* Gained and released another reference, retry. */
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goto retry;
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}
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next = atomic_cas_uint(&vp->v_usecount, use, use - 1);
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if (__predict_true(next == use)) {
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if (__predict_false((use & VUSECOUNT_MASK) != 1)) {
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/* Gained another reference. */
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mutex_exit(vp->v_interlock);
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return;
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}
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break;
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}
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}
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if (VSTATE_GET(vp) == VS_RECLAIMED && vp->v_holdcnt == 0) {
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@ -1399,7 +1422,8 @@ vcache_tryvget(vnode_t *vp)
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if (__predict_false((use & VUSECOUNT_GATE) == 0)) {
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return EBUSY;
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}
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next = atomic_cas_uint(&vp->v_usecount, use, use + 1);
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next = atomic_cas_uint(&vp->v_usecount,
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use, (use + 1) | VUSECOUNT_VGET);
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if (__predict_true(next == use)) {
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return 0;
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}
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@ -1416,6 +1440,7 @@ vcache_tryvget(vnode_t *vp)
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int
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vcache_vget(vnode_t *vp)
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{
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int error;
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KASSERT(mutex_owned(vp->v_interlock));
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@ -1433,7 +1458,8 @@ vcache_vget(vnode_t *vp)
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return ENOENT;
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}
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VSTATE_ASSERT(vp, VS_LOADED);
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atomic_inc_uint(&vp->v_usecount);
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error = vcache_tryvget(vp);
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KASSERT(error == 0);
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mutex_exit(vp->v_interlock);
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return 0;
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@ -1,4 +1,4 @@
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/* $NetBSD: pstat.c,v 1.133 2021/11/27 22:30:26 rillig Exp $ */
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/* $NetBSD: pstat.c,v 1.134 2022/02/17 14:39:14 hannken Exp $ */
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/*-
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* Copyright (c) 1980, 1991, 1993, 1994
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@ -39,7 +39,7 @@ __COPYRIGHT("@(#) Copyright (c) 1980, 1991, 1993, 1994\
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#if 0
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static char sccsid[] = "@(#)pstat.c 8.16 (Berkeley) 5/9/95";
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#else
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__RCSID("$NetBSD: pstat.c,v 1.133 2021/11/27 22:30:26 rillig Exp $");
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__RCSID("$NetBSD: pstat.c,v 1.134 2022/02/17 14:39:14 hannken Exp $");
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#endif
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#endif /* not lint */
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@ -444,7 +444,7 @@ vnode_print(struct vnode *avnode, struct vnode *vp)
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PRWORD(ovflw, "%*lx", PTRSTRWIDTH, 0, (long)avnode);
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PRWORD(ovflw, " %*s", 4, 1, type);
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PRWORD(ovflw, " %*s", 6, 1, flags);
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#define VUSECOUNT_MASK 0x7fffffff /* XXX: kernel private */
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#define VUSECOUNT_MASK 0x3fffffff /* XXX: kernel private */
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PRWORD(ovflw, " %*d", 5, 1, vp->v_usecount & VUSECOUNT_MASK);
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PRWORD(ovflw, " %*d", 5, 1, vp->v_holdcnt);
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PRWORD(ovflw, " %*d", 4, 1, vp->v_tag);
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