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Date:      Thu, 28 Jul 2016 15:57:01 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r303448 - head/sys/vm
Message-ID:  <201607281557.u6SFv1aE020276@repo.freebsd.org>
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Author: kib
Date: Thu Jul 28 15:57:01 2016
New Revision: 303448
URL: https://svnweb.freebsd.org/changeset/base/303448

Log:
  Do not delegate a work to geom event thread which can be done inline.
  
  In particular, swapongeom_ev() needed event thread context when swap
  pager configuration was performed under Giant and geom asserted that
  Giant is not owned.  Now both of the reason went away.
  
  On the other hand, note that swpageom_release() is called from the
  bio_done context, and possible close cannot be performed inline.
  
  Also fix some minor issues.  The swapgeom() function does not use the
  td argument, remove it.  Recheck that the vnode passed is still VCHR
  and not reclaimed after the lock.
  
  Reviewed by:	mav
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks

Modified:
  head/sys/vm/swap_pager.c

Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c	Thu Jul 28 15:54:17 2016	(r303447)
+++ head/sys/vm/swap_pager.c	Thu Jul 28 15:57:01 2016	(r303448)
@@ -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) {
@@ -2560,17 +2560,9 @@ swapgeom_close(struct thread *td, struct
 		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 +2570,15 @@ 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 +2595,31 @@ 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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