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Date:      Fri, 2 Dec 2016 18:03:15 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r309425 - head/sys/kern
Message-ID:  <201612021803.uB2I3Fmt046712@repo.freebsd.org>
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Author: mjg
Date: Fri Dec  2 18:03:15 2016
New Revision: 309425
URL: https://svnweb.freebsd.org/changeset/base/309425

Log:
  vfs: provide fake locking primitives for the crossmp vnode
  
  Since the vnode is only expected to be shared locked, we can save a
  little overhead by only pretending we are locking in the first place.
  
  Reviewed by:	kib
  Tested by:	pho

Modified:
  head/sys/kern/vfs_lookup.c

Modified: head/sys/kern/vfs_lookup.c
==============================================================================
--- head/sys/kern/vfs_lookup.c	Fri Dec  2 17:08:27 2016	(r309424)
+++ head/sys/kern/vfs_lookup.c	Fri Dec  2 18:03:15 2016	(r309425)
@@ -79,6 +79,64 @@ uma_zone_t namei_zone;
 /* Placeholder vnode for mp traversal. */
 static struct vnode *vp_crossmp;
 
+static int
+crossmp_vop_islocked(struct vop_islocked_args *ap)
+{
+
+	return (LK_SHARED);
+}
+
+static int
+crossmp_vop_lock1(struct vop_lock1_args *ap)
+{
+	struct vnode *vp;
+	struct lock *lk;
+	const char *file;
+	int flags, line;
+
+	vp = ap->a_vp;
+	lk = vp->v_vnlock;
+	flags = ap->a_flags;
+	file = ap->a_file;
+	line = ap->a_line;
+
+	if ((flags & LK_SHARED) == 0)
+		panic("invalid lock request for crossmp");
+
+	WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, file, line,
+	    flags & LK_INTERLOCK ? &VI_MTX(vp)->lock_object : NULL);
+	WITNESS_LOCK(&lk->lock_object, 0, file, line);
+	if ((flags & LK_INTERLOCK) != 0)
+		VI_UNLOCK(vp);
+	LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, ap->a_file, line);
+	return (0);
+}
+
+static int
+crossmp_vop_unlock(struct vop_unlock_args *ap)
+{
+	struct vnode *vp;
+	struct lock *lk;
+	int flags;
+
+	vp = ap->a_vp;
+	lk = vp->v_vnlock;
+	flags = ap->a_flags;
+
+	if ((flags & LK_INTERLOCK) != 0)
+		VI_UNLOCK(vp);
+	WITNESS_UNLOCK(&lk->lock_object, 0, LOCK_FILE, LOCK_LINE);
+	LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, LOCK_FILE,
+	    LOCK_LINE);
+	return (0);
+}
+
+static struct vop_vector crossmp_vnodeops = {
+	.vop_islocked =		crossmp_vop_islocked,
+	.vop_lock1 =		crossmp_vop_lock1,
+	.vop_unlock =		crossmp_vop_unlock,
+};
+
 struct nameicap_tracker {
 	struct vnode *dp;
 	TAILQ_ENTRY(nameicap_tracker) nm_link;
@@ -95,10 +153,7 @@ nameiinit(void *dummy __unused)
 	    UMA_ALIGN_PTR, 0);
 	nt_zone = uma_zcreate("rentr", sizeof(struct nameicap_tracker),
 	    NULL, NULL, NULL, NULL, sizeof(void *), 0);
-	getnewvnode("crossmp", NULL, &dead_vnodeops, &vp_crossmp);
-	vn_lock(vp_crossmp, LK_EXCLUSIVE);
-	VN_LOCK_ASHARE(vp_crossmp);
-	VOP_UNLOCK(vp_crossmp, 0);
+	getnewvnode("crossmp", NULL, &crossmp_vnodeops, &vp_crossmp);
 }
 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_SECOND, nameiinit, NULL);

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