diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 80e4d107726..945d95d9a7a 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -318,7 +318,7 @@ bufspacewakeup(void)
  * runningbufwakeup() - in-progress I/O accounting.
  *
  */
-static __inline void
+void
 runningbufwakeup(struct buf *bp)
 {
 
@@ -847,8 +847,7 @@ bufwrite(struct buf *bp)
 		 * or syncer daemon trying to clean up as that can lead
 		 * to deadlock.
 		 */
-		if (curthread->td_proc != bufdaemonproc &&
-		    curthread->td_proc != updateproc)
+		if ((curthread->td_pflags & TDP_NORUNNINGBUF) == 0)
 			waitrunningbufspace();
 	}
 
@@ -1964,6 +1963,7 @@ buf_daemon()
 	/*
 	 * This process is allowed to take the buffer cache to the limit
 	 */
+	curthread->td_pflags |= TDP_NORUNNINGBUF;
 	mtx_lock(&bdlock);
 	for (;;) {
 		bd_request = 0;
diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index 3486b0c1c66..26d5b9f0e90 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -1524,7 +1524,7 @@ sysctl_vfs_worklist_len(SYSCTL_HANDLER_ARGS)
 SYSCTL_PROC(_vfs, OID_AUTO, worklist_len, CTLTYPE_INT | CTLFLAG_RD, NULL, 0,
     sysctl_vfs_worklist_len, "I", "Syncer thread worklist length");
 
-struct  proc *updateproc;
+static struct proc *updateproc;
 static void sched_sync(void);
 static struct kproc_desc up_kp = {
 	"syncer",
@@ -1601,6 +1601,7 @@ sched_sync(void)
 	first_printf = 1;
 	syncer_state = SYNCER_RUNNING;
 	starttime = time_uptime;
+	td->td_pflags |= TDP_NORUNNINGBUF;
 
 	EVENTHANDLER_REGISTER(shutdown_pre_sync, syncer_shutdown, td->td_proc,
 	    SHUTDOWN_PRI_LAST);
diff --git a/sys/sys/buf.h b/sys/sys/buf.h
index 63405122deb..6ef4f0f8655 100644
--- a/sys/sys/buf.h
+++ b/sys/sys/buf.h
@@ -477,6 +477,7 @@ extern int	nswbuf;			/* Number of swap I/O buffer headers. */
 extern int	cluster_pbuf_freecnt;	/* Number of pbufs for clusters */
 extern int	vnode_pbuf_freecnt;	/* Number of pbufs for vnode pager */
 
+void	runningbufwakeup(struct buf *);
 caddr_t	kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est);
 void	bufinit(void);
 void	bwillwrite(void);
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 40275bc8c6b..1006b9b8735 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -378,6 +378,7 @@ struct thread {
 #define	TDP_SCHED4	0x00008000 /* Reserved for scheduler private use */
 #define	TDP_GEOM	0x00010000 /* Settle GEOM before finishing syscall */
 #define	TDP_SOFTDEP	0x00020000 /* Stuck processing softdep worklist */
+#define	TDP_NORUNNINGBUF 0x00040000 /* Ignore runningbufspace check */
 
 /*
  * Reasons that the current thread can not be run yet.
@@ -833,7 +834,6 @@ TAILQ_HEAD(threadqueue, thread);
 extern struct proclist allproc;		/* List of all processes. */
 extern struct proclist zombproc;	/* List of zombie processes. */
 extern struct proc *initproc, *pageproc; /* Process slots for init, pager. */
-extern struct proc *updateproc;		/* Process slot for syncer (sic). */
 
 extern struct uma_zone *proc_zone;
 
diff --git a/sys/ufs/ffs/ffs_snapshot.c b/sys/ufs/ffs/ffs_snapshot.c
index c1344611e7d..3e7e2311f0e 100644
--- a/sys/ufs/ffs/ffs_snapshot.c
+++ b/sys/ufs/ffs/ffs_snapshot.c
@@ -1997,6 +1997,12 @@ ffs_copyonwrite(devvp, bp)
 		VI_UNLOCK(devvp);
 		return (0);
 	}
+	/*
+	 * Since I/O on bp isn't yet in progress and it may be blocked
+	 * for a long time waiting on snaplk, back it out of
+	 * runningbufspace, possibly waking other threads waiting for space.
+	 */
+	runningbufwakeup(bp);
 	/*
 	 * Not in the precomputed list, so check the snapshots.
 	 */
@@ -2028,7 +2034,7 @@ retry:
 				goto retry;
 			}
 			snapshot_locked = 1;
-			td->td_pflags |= TDP_COWINPROGRESS;
+			td->td_pflags |= TDP_COWINPROGRESS | TDP_NORUNNINGBUF;
 			error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
 			   fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
 			td->td_pflags &= ~TDP_COWINPROGRESS;
@@ -2065,7 +2071,7 @@ retry:
 			goto retry;
 		}
 		snapshot_locked = 1;
-		td->td_pflags |= TDP_COWINPROGRESS;
+		td->td_pflags |= TDP_COWINPROGRESS | TDP_NORUNNINGBUF;
 		error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
 		    fs->fs_bsize, KERNCRED, 0, &cbp);
 		td->td_pflags &= ~TDP_COWINPROGRESS;
@@ -2120,10 +2126,16 @@ retry:
 		if (dopersistence && VTOI(vp)->i_effnlink > 0)
 			(void) ffs_syncvnode(vp, MNT_WAIT);
 	}
-	if (snapshot_locked)
+	if (snapshot_locked) {
 		lockmgr(vp->v_vnlock, LK_RELEASE, NULL, td);
-	else
+		td->td_pflags &= ~TDP_NORUNNINGBUF;
+	} else
 		VI_UNLOCK(devvp);
+	/*
+	 * I/O on bp will now be started, so count it in runningbufspace.
+	 */
+	if (bp->b_runningbufspace)
+		atomic_add_int(&runningbufspace, bp->b_runningbufspace);
 	return (error);
 }