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Date:      Wed, 10 Aug 2016 12:11:12 +0000 (UTC)
From:      Konstantin Belousov <kib@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: r303905 - stable/11/sys/vm
Message-ID:  <201608101211.u7ACBC0j039360@repo.freebsd.org>
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Author: kib
Date: Wed Aug 10 12:11:11 2016
New Revision: 303905
URL: https://svnweb.freebsd.org/changeset/base/303905

Log:
  MFC r303448:
  Do not delegate a work to geom event thread which can be done inline.
  
  MFC r303703:
  Explain why swapgeom_close_ev() is delegated.
  
  Approved by:	re (gjb)

Modified:
  stable/11/sys/vm/swap_pager.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/vm/swap_pager.c
==============================================================================
--- stable/11/sys/vm/swap_pager.c	Wed Aug 10 10:36:11 2016	(r303904)
+++ stable/11/sys/vm/swap_pager.c	Wed Aug 10 12:11:11 2016	(r303905)
@@ -395,7 +395,7 @@ SYSCTL_INT(_vm, OID_AUTO, dmmax, CTLFLAG
 
 static void	swp_sizecheck(void);
 static void	swp_pager_async_iodone(struct buf *bp);
-static int	swapongeom(struct thread *, struct vnode *);
+static int	swapongeom(struct vnode *);
 static int	swaponvp(struct thread *, struct vnode *, u_long);
 static int	swapoff_one(struct swdevt *sp, struct ucred *cred);
 
@@ -2019,7 +2019,7 @@ sys_swapon(struct thread *td, struct swa
 	vp = nd.ni_vp;
 
 	if (vn_isdisk(vp, &error)) {
-		error = swapongeom(td, vp);
+		error = swapongeom(vp);
 	} else if (vp->v_type == VREG &&
 	    (vp->v_mount->mnt_vfc->vfc_flags & VFCF_NETWORK) != 0 &&
 	    (error = VOP_GETATTR(vp, &attr, td->td_ucred)) == 0) {
@@ -2431,8 +2431,9 @@ swapgeom_acquire(struct g_consumer *cp)
 }
 
 /*
- * Remove a reference from the g_consumer. Post a close event if
- * all references go away.
+ * Remove a reference from the g_consumer.  Post a close event if all
+ * references go away, since the function might be called from the
+ * biodone context.
  */
 static void
 swapgeom_release(struct g_consumer *cp, struct swdevt *sp)
@@ -2555,22 +2556,19 @@ swapgeom_close(struct thread *td, struct
 	cp = sw->sw_id;
 	sw->sw_id = NULL;
 	mtx_unlock(&sw_dev_mtx);
-	/* XXX: direct call when Giant untangled */
+
+	/*
+	 * swapgeom_close() may be called from the biodone context,
+	 * where we cannot perform topology changes.  Delegate the
+	 * work to the events thread.
+	 */
 	if (cp != NULL)
 		g_waitfor_event(swapgeom_close_ev, cp, M_WAITOK, NULL);
 }
 
-
-struct swh0h0 {
-	struct cdev *dev;
-	struct vnode *vp;
-	int	error;
-};
-
-static void
-swapongeom_ev(void *arg, int flags)
+static int
+swapongeom_locked(struct cdev *dev, struct vnode *vp)
 {
-	struct swh0h0 *swh;
 	struct g_provider *pp;
 	struct g_consumer *cp;
 	static struct g_geom *gp;
@@ -2578,20 +2576,15 @@ swapongeom_ev(void *arg, int flags)
 	u_long nblks;
 	int error;
 
-	swh = arg;
-	swh->error = 0;
-	pp = g_dev_getprovider(swh->dev);
-	if (pp == NULL) {
-		swh->error = ENODEV;
-		return;
-	}
+	pp = g_dev_getprovider(dev);
+	if (pp == NULL)
+		return (ENODEV);
 	mtx_lock(&sw_dev_mtx);
 	TAILQ_FOREACH(sp, &swtailq, sw_list) {
 		cp = sp->sw_id;
 		if (cp != NULL && cp->provider == pp) {
 			mtx_unlock(&sw_dev_mtx);
-			swh->error = EBUSY;
-			return;
+			return (EBUSY);
 		}
 	}
 	mtx_unlock(&sw_dev_mtx);
@@ -2608,34 +2601,31 @@ swapongeom_ev(void *arg, int flags)
 	 * set an exclusive count :-(
 	 */
 	error = g_access(cp, 1, 1, 0);
-	if (error) {
+	if (error != 0) {
 		g_detach(cp);
 		g_destroy_consumer(cp);
-		swh->error = error;
-		return;
+		return (error);
 	}
 	nblks = pp->mediasize / DEV_BSIZE;
-	swaponsomething(swh->vp, cp, nblks, swapgeom_strategy,
-	    swapgeom_close, dev2udev(swh->dev),
+	swaponsomething(vp, cp, nblks, swapgeom_strategy,
+	    swapgeom_close, dev2udev(dev),
 	    (pp->flags & G_PF_ACCEPT_UNMAPPED) != 0 ? SW_UNMAPPED : 0);
-	swh->error = 0;
+	return (0);
 }
 
 static int
-swapongeom(struct thread *td, struct vnode *vp)
+swapongeom(struct vnode *vp)
 {
 	int error;
-	struct swh0h0 swh;
 
 	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
-
-	swh.dev = vp->v_rdev;
-	swh.vp = vp;
-	swh.error = 0;
-	/* XXX: direct call when Giant untangled */
-	error = g_waitfor_event(swapongeom_ev, &swh, M_WAITOK, NULL);
-	if (!error)
-		error = swh.error;
+	if (vp->v_type != VCHR || (vp->v_iflag & VI_DOOMED) != 0) {
+		error = ENOENT;
+	} else {
+		g_topology_lock();
+		error = swapongeom_locked(vp->v_rdev, vp);
+		g_topology_unlock();
+	}
 	VOP_UNLOCK(vp, 0);
 	return (error);
 }

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