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Date:      Sun, 5 Nov 2017 22:28:39 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r325456 - head/sys/kern
Message-ID:  <201711052228.vA5MSdqH006971@repo.freebsd.org>
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Author: mjg
Date: Sun Nov  5 22:28:39 2017
New Revision: 325456
URL: https://svnweb.freebsd.org/changeset/base/325456

Log:
  namecache: wlock buckets in cache_lookup_nomakeentry
  
  Since the case of an empty chain was already covered, it si very likely
  that the existing entry is matching. Skipping readlocking saves on lock
  upgrade.

Modified:
  head/sys/kern/vfs_cache.c

Modified: head/sys/kern/vfs_cache.c
==============================================================================
--- head/sys/kern/vfs_cache.c	Sun Nov  5 22:22:22 2017	(r325455)
+++ head/sys/kern/vfs_cache.c	Sun Nov  5 22:28:39 2017	(r325456)
@@ -984,6 +984,28 @@ out:
 }
 
 static int
+cache_zap_wlocked_bucket(struct namecache *ncp, struct rwlock *blp)
+{
+	struct mtx *dvlp, *vlp;
+
+	cache_assert_bucket_locked(ncp, RA_WLOCKED);
+
+	dvlp = VP2VNODELOCK(ncp->nc_dvp);
+	vlp = NULL;
+	if (!(ncp->nc_flag & NCF_NEGATIVE))
+		vlp = VP2VNODELOCK(ncp->nc_vp);
+	if (cache_trylock_vnodes(dvlp, vlp) == 0) {
+		cache_zap_locked(ncp, false);
+		rw_wunlock(blp);
+		cache_unlock_vnodes(dvlp, vlp);
+		return (0);
+	}
+
+	rw_wunlock(blp);
+	return (EAGAIN);
+}
+
+static int
 cache_zap_rlocked_bucket(struct namecache *ncp, struct rwlock *blp)
 {
 	struct mtx *dvlp, *vlp;
@@ -1166,7 +1188,7 @@ retry:
 	if (LIST_EMPTY(NCHHASH(hash)))
 		goto out_no_entry;
 
-	rw_rlock(blp);
+	rw_wlock(blp);
 
 	LIST_FOREACH(ncp, (NCHHASH(hash)), nc_hash) {
 		counter_u64_add(numchecks, 1);
@@ -1177,13 +1199,13 @@ retry:
 
 	/* We failed to find an entry */
 	if (ncp == NULL) {
-		rw_runlock(blp);
+		rw_wunlock(blp);
 		goto out_no_entry;
 	}
 
 	counter_u64_add(numposzaps, 1);
 
-	error = cache_zap_rlocked_bucket(ncp, blp);
+	error = cache_zap_wlocked_bucket(ncp, blp);
 	if (error != 0) {
 		zap_and_exit_bucket_fail++;
 		cache_maybe_yield();

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