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Date:      Wed, 25 Oct 2017 01:07:45 +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: r324967 - stable/11/sys/kern
Message-ID:  <201710250107.v9P17jWq059175@repo.freebsd.org>
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Author: markj
Date: Wed Oct 25 01:07:45 2017
New Revision: 324967
URL: https://svnweb.freebsd.org/changeset/base/324967

Log:
  MFC r324704:
  Fix a racy VI_DOOMED check in MNT_VNODE_FOREACH_ALL().

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 Oct 25 01:07:12 2017	(r324966)
+++ stable/11/sys/kern/vfs_subr.c	Wed Oct 25 01:07:45 2017	(r324967)
@@ -5201,12 +5201,18 @@ __mnt_vnode_next_all(struct vnode **mvp, struct mount 
 		kern_yield(PRI_USER);
 	MNT_ILOCK(mp);
 	KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
-	vp = TAILQ_NEXT(*mvp, v_nmntvnodes);
-	while (vp != NULL && (vp->v_type == VMARKER ||
-	    (vp->v_iflag & VI_DOOMED) != 0))
-		vp = TAILQ_NEXT(vp, v_nmntvnodes);
-
-	/* Check if we are done */
+	for (vp = TAILQ_NEXT(*mvp, v_nmntvnodes); vp != NULL;
+	    vp = TAILQ_NEXT(vp, v_nmntvnodes)) {
+		/* Allow a racy peek at VI_DOOMED to save a lock acquisition. */
+		if (vp->v_type == VMARKER || (vp->v_iflag & VI_DOOMED) != 0)
+			continue;
+		VI_LOCK(vp);
+		if ((vp->v_iflag & VI_DOOMED) != 0) {
+			VI_UNLOCK(vp);
+			continue;
+		}
+		break;
+	}
 	if (vp == NULL) {
 		__mnt_vnode_markerfree_all(mvp, mp);
 		/* MNT_IUNLOCK(mp); -- done in above function */
@@ -5215,7 +5221,6 @@ __mnt_vnode_next_all(struct vnode **mvp, struct mount 
 	}
 	TAILQ_REMOVE(&mp->mnt_nvnodelist, *mvp, v_nmntvnodes);
 	TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
-	VI_LOCK(vp);
 	MNT_IUNLOCK(mp);
 	return (vp);
 }
@@ -5228,14 +5233,20 @@ __mnt_vnode_first_all(struct vnode **mvp, struct mount
 	*mvp = malloc(sizeof(struct vnode), M_VNODE_MARKER, M_WAITOK | M_ZERO);
 	MNT_ILOCK(mp);
 	MNT_REF(mp);
+	(*mvp)->v_mount = mp;
 	(*mvp)->v_type = VMARKER;
 
-	vp = TAILQ_FIRST(&mp->mnt_nvnodelist);
-	while (vp != NULL && (vp->v_type == VMARKER ||
-	    (vp->v_iflag & VI_DOOMED) != 0))
-		vp = TAILQ_NEXT(vp, v_nmntvnodes);
-
-	/* Check if we are done */
+	TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
+		/* Allow a racy peek at VI_DOOMED to save a lock acquisition. */
+		if (vp->v_type == VMARKER || (vp->v_iflag & VI_DOOMED) != 0)
+			continue;
+		VI_LOCK(vp);
+		if ((vp->v_iflag & VI_DOOMED) != 0) {
+			VI_UNLOCK(vp);
+			continue;
+		}
+		break;
+	}
 	if (vp == NULL) {
 		MNT_REL(mp);
 		MNT_IUNLOCK(mp);
@@ -5243,13 +5254,10 @@ __mnt_vnode_first_all(struct vnode **mvp, struct mount
 		*mvp = NULL;
 		return (NULL);
 	}
-	(*mvp)->v_mount = mp;
 	TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
-	VI_LOCK(vp);
 	MNT_IUNLOCK(mp);
 	return (vp);
 }
-
 
 void
 __mnt_vnode_markerfree_all(struct vnode **mvp, struct mount *mp)

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