bc855512c8
that they set v->v_vnlock. This is true for all filesystems in the tree. - Remove all uses of LK_THISLAYER. If the lower layer is locked, the null layer is locked. We only use vget() to get a reference now. null essentially does no locking. This fixes LOOKUP_SHARED with nullfs. - Remove the special LK_DRAIN considerations, I do not believe this is needed now as LK_DRAIN doesn't destroy the lower vnode's lock, and it's hardly used anymore. - Add one well commented hack to prevent the lowervp from going away while we're in it's VOP_LOCK routine. This can only happen if we're forcibly unmounted while some callers are waiting in the lock. In this case the lowervp could be recycled after we drop our last ref in null_reclaim(). Prevent this with a vhold().
326 lines
8.4 KiB
C
326 lines
8.4 KiB
C
/*-
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software donated to Berkeley by
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* Jan-Simon Pendry.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)null_subr.c 8.7 (Berkeley) 5/14/95
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*
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* $FreeBSD$
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/malloc.h>
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#include <sys/mount.h>
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#include <sys/proc.h>
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#include <sys/vnode.h>
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#include <fs/nullfs/null.h>
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#define LOG2_SIZEVNODE 8 /* log2(sizeof struct vnode) */
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#define NNULLNODECACHE 16
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/*
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* Null layer cache:
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* Each cache entry holds a reference to the lower vnode
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* along with a pointer to the alias vnode. When an
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* entry is added the lower vnode is VREF'd. When the
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* alias is removed the lower vnode is vrele'd.
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*/
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#define NULL_NHASH(vp) \
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(&null_node_hashtbl[(((uintptr_t)vp)>>LOG2_SIZEVNODE) & null_node_hash])
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static LIST_HEAD(null_node_hashhead, null_node) *null_node_hashtbl;
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static u_long null_node_hash;
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struct mtx null_hashmtx;
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static MALLOC_DEFINE(M_NULLFSHASH, "NULLFS hash", "NULLFS hash table");
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MALLOC_DEFINE(M_NULLFSNODE, "NULLFS node", "NULLFS vnode private part");
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static struct vnode * null_hashget(struct mount *, struct vnode *);
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static struct vnode * null_hashins(struct mount *, struct null_node *);
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/*
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* Initialise cache headers
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*/
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int
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nullfs_init(vfsp)
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struct vfsconf *vfsp;
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{
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NULLFSDEBUG("nullfs_init\n"); /* printed during system boot */
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null_node_hashtbl = hashinit(NNULLNODECACHE, M_NULLFSHASH, &null_node_hash);
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mtx_init(&null_hashmtx, "nullhs", NULL, MTX_DEF);
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return (0);
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}
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int
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nullfs_uninit(vfsp)
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struct vfsconf *vfsp;
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{
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mtx_destroy(&null_hashmtx);
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free(null_node_hashtbl, M_NULLFSHASH);
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return (0);
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}
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/*
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* Return a VREF'ed alias for lower vnode if already exists, else 0.
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* Lower vnode should be locked on entry and will be left locked on exit.
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*/
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static struct vnode *
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null_hashget(mp, lowervp)
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struct mount *mp;
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struct vnode *lowervp;
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{
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struct thread *td = curthread; /* XXX */
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struct null_node_hashhead *hd;
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struct null_node *a;
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struct vnode *vp;
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/*
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* Find hash base, and then search the (two-way) linked
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* list looking for a null_node structure which is referencing
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* the lower vnode. If found, the increment the null_node
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* reference count (but NOT the lower vnode's VREF counter).
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*/
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hd = NULL_NHASH(lowervp);
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loop:
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mtx_lock(&null_hashmtx);
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LIST_FOREACH(a, hd, null_hash) {
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if (a->null_lowervp == lowervp && NULLTOV(a)->v_mount == mp) {
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vp = NULLTOV(a);
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VI_LOCK(vp);
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/*
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* If the nullfs node is being recycled we have
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* to wait until it finishes prior to scanning
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* again.
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*/
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mtx_unlock(&null_hashmtx);
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if ((vp->v_iflag & VI_DOOMED) != 0) {
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/* Wait for recycling to finish. */
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VOP_LOCK(vp, LK_EXCLUSIVE|LK_INTERLOCK, td);
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VOP_UNLOCK(vp, 0, td);
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goto loop;
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}
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vget(vp, LK_INTERLOCK, td);
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return (vp);
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}
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}
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mtx_unlock(&null_hashmtx);
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return (NULLVP);
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}
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/*
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* Act like null_hashget, but add passed null_node to hash if no existing
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* node found.
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*/
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static struct vnode *
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null_hashins(mp, xp)
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struct mount *mp;
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struct null_node *xp;
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{
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struct thread *td = curthread; /* XXX */
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struct null_node_hashhead *hd;
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struct null_node *oxp;
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struct vnode *ovp;
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hd = NULL_NHASH(xp->null_lowervp);
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loop:
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mtx_lock(&null_hashmtx);
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LIST_FOREACH(oxp, hd, null_hash) {
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if (oxp->null_lowervp == xp->null_lowervp &&
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NULLTOV(oxp)->v_mount == mp) {
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ovp = NULLTOV(oxp);
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VI_LOCK(ovp);
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/*
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* If the nullfs node is being recycled we have
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* to wait until it finishes prior to scanning
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* again.
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*/
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mtx_unlock(&null_hashmtx);
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if ((ovp->v_iflag & VI_DOOMED) != 0) {
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VOP_LOCK(ovp, LK_EXCLUSIVE|LK_INTERLOCK, td);
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VOP_UNLOCK(ovp, 0, td);
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goto loop;
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}
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vget(ovp, LK_INTERLOCK, td);
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return (ovp);
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}
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}
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LIST_INSERT_HEAD(hd, xp, null_hash);
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mtx_unlock(&null_hashmtx);
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return (NULLVP);
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}
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/*
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* Make a new or get existing nullfs node.
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* Vp is the alias vnode, lowervp is the lower vnode.
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*
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* The lowervp assumed to be locked and having "spare" reference. This routine
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* vrele lowervp if nullfs node was taken from hash. Otherwise it "transfers"
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* the caller's "spare" reference to created nullfs vnode.
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*/
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int
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null_nodeget(mp, lowervp, vpp)
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struct mount *mp;
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struct vnode *lowervp;
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struct vnode **vpp;
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{
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struct null_node *xp;
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struct vnode *vp;
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int error;
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/* Lookup the hash firstly */
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*vpp = null_hashget(mp, lowervp);
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if (*vpp != NULL) {
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vrele(lowervp);
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return (0);
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}
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/*
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* We do not serialize vnode creation, instead we will check for
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* duplicates later, when adding new vnode to hash.
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*
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* Note that duplicate can only appear in hash if the lowervp is
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* locked LK_SHARED.
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*/
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/*
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* Do the MALLOC before the getnewvnode since doing so afterward
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* might cause a bogus v_data pointer to get dereferenced
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* elsewhere if MALLOC should block.
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*/
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MALLOC(xp, struct null_node *, sizeof(struct null_node),
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M_NULLFSNODE, M_WAITOK);
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error = getnewvnode("null", mp, &null_vnodeops, &vp);
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if (error) {
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FREE(xp, M_NULLFSNODE);
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return (error);
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}
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xp->null_vnode = vp;
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xp->null_lowervp = lowervp;
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vp->v_type = lowervp->v_type;
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vp->v_data = xp;
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vp->v_vnlock = lowervp->v_vnlock;
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if (vp->v_vnlock == NULL)
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panic("null_nodeget: Passed a NULL vnlock.\n");
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/*
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* Atomically insert our new node into the hash or vget existing
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* if someone else has beaten us to it.
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*/
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*vpp = null_hashins(mp, xp);
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if (*vpp != NULL) {
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vrele(lowervp);
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vp->v_vnlock = &vp->v_lock;
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xp->null_lowervp = NULL;
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vrele(vp);
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return (0);
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}
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*vpp = vp;
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return (0);
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}
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/*
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* Remove node from hash.
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*/
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void
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null_hashrem(xp)
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struct null_node *xp;
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{
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mtx_lock(&null_hashmtx);
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LIST_REMOVE(xp, null_hash);
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mtx_unlock(&null_hashmtx);
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}
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#ifdef DIAGNOSTIC
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#ifdef KDB
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#define null_checkvp_barrier 1
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#else
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#define null_checkvp_barrier 0
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#endif
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struct vnode *
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null_checkvp(vp, fil, lno)
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struct vnode *vp;
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char *fil;
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int lno;
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{
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struct null_node *a = VTONULL(vp);
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#ifdef notyet
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/*
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* Can't do this check because vop_reclaim runs
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* with a funny vop vector.
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*/
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if (vp->v_op != null_vnodeop_p) {
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printf ("null_checkvp: on non-null-node\n");
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while (null_checkvp_barrier) /*WAIT*/ ;
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panic("null_checkvp");
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};
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#endif
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if (a->null_lowervp == NULLVP) {
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/* Should never happen */
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int i; u_long *p;
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printf("vp = %p, ZERO ptr\n", (void *)vp);
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for (p = (u_long *) a, i = 0; i < 8; i++)
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printf(" %lx", p[i]);
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printf("\n");
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/* wait for debugger */
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while (null_checkvp_barrier) /*WAIT*/ ;
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panic("null_checkvp");
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}
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if (vrefcnt(a->null_lowervp) < 1) {
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int i; u_long *p;
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printf("vp = %p, unref'ed lowervp\n", (void *)vp);
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for (p = (u_long *) a, i = 0; i < 8; i++)
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printf(" %lx", p[i]);
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printf("\n");
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/* wait for debugger */
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while (null_checkvp_barrier) /*WAIT*/ ;
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panic ("null with unref'ed lowervp");
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};
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#ifdef notyet
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printf("null %x/%d -> %x/%d [%s, %d]\n",
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NULLTOV(a), vrefcnt(NULLTOV(a)),
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a->null_lowervp, vrefcnt(a->null_lowervp),
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fil, lno);
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#endif
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return a->null_lowervp;
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}
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#endif
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