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From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Thu, 21 Jan 2016 01:07:05 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: svn commit: r294477 - head/sys/kern
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Author: mjg
Date: Thu Jan 21 01:07:05 2016
New Revision: 294477
URL: https://svnweb.freebsd.org/changeset/base/294477

Log:
  cache: perform . lockup without the namecache lock
  
  Reviewed by:	kib

Modified:
  head/sys/kern/vfs_cache.c

Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c	Thu Jan 21 01:05:41 2016	(r294476)
+++ head/sys/kern/vfs_cache.c	Thu Jan 21 01:07:05 2016	(r294477)
@@ -508,7 +508,6 @@ cache_lookup(struct vnode *dvp, struct v
 		return (0);
 	}
 retry:
-	CACHE_RLOCK();
 	wlocked = 0;
 	counter_u64_add(numcalls, 1);
 	error = 0;
@@ -525,8 +524,28 @@ retry_wlocked:
 				timespecclear(tsp);
 			if (ticksp != NULL)
 				*ticksp = ticks;
-			goto success;
+			VREF(*vpp);
+			/*
+			 * When we lookup "." we still can be asked to lock it
+			 * differently...
+			 */
+			ltype = cnp->cn_lkflags & LK_TYPE_MASK;
+			if (ltype != VOP_ISLOCKED(*vpp)) {
+				if (ltype == LK_EXCLUSIVE) {
+					vn_lock(*vpp, LK_UPGRADE | LK_RETRY);
+					if ((*vpp)->v_iflag & VI_DOOMED) {
+						/* forced unmount */
+						vrele(*vpp);
+						*vpp = NULL;
+						return (ENOENT);
+					}
+				} else
+					vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
+			}
+			return (-1);
 		}
+		if (!wlocked)
+			CACHE_RLOCK();
 		if (cnp->cn_namelen == 2 && cnp->cn_nameptr[1] == '.') {
 			counter_u64_add(dotdothits, 1);
 			if (dvp->v_cache_dd == NULL) {
@@ -562,7 +581,8 @@ retry_wlocked:
 				    nc_dotdottime;
 			goto success;
 		}
-	}
+	} else if (!wlocked)
+		CACHE_RLOCK();
 
 	hash = cache_get_hash(cnp->cn_nameptr, cnp->cn_namelen, dvp);
 	LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
@@ -652,31 +672,7 @@ success:
 	 * On success we return a locked and ref'd vnode as per the lookup
 	 * protocol.
 	 */
-	if (dvp == *vpp) {   /* lookup on "." */
-		VREF(*vpp);
-		if (wlocked)
-			CACHE_WUNLOCK();
-		else
-			CACHE_RUNLOCK();
-		/*
-		 * When we lookup "." we still can be asked to lock it
-		 * differently...
-		 */
-		ltype = cnp->cn_lkflags & LK_TYPE_MASK;
-		if (ltype != VOP_ISLOCKED(*vpp)) {
-			if (ltype == LK_EXCLUSIVE) {
-				vn_lock(*vpp, LK_UPGRADE | LK_RETRY);
-				if ((*vpp)->v_iflag & VI_DOOMED) {
-					/* forced unmount */
-					vrele(*vpp);
-					*vpp = NULL;
-					return (ENOENT);
-				}
-			} else
-				vn_lock(*vpp, LK_DOWNGRADE | LK_RETRY);
-		}
-		return (-1);
-	}
+	MPASS(dvp != *vpp);
 	ltype = 0;	/* silence gcc warning */
 	if (cnp->cn_flags & ISDOTDOT) {
 		ltype = VOP_ISLOCKED(dvp);