[src/trunk]: src/sys/kern cache_enter: concurrent lookups in the same directo...

[pk <pk%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5f958e204b08
branches:  trunk
changeset: 566255:5f958e204b08
user:      pk <pk%NetBSD.org@localhost>
date:      Sun May 02 12:00:34 2004 +0000

description:
cache_enter: concurrent lookups in the same directory may race for a
cache entry. Upon detection, free our tentative entry and return.

diffstat:

 sys/kern/vfs_cache.c |  18 ++++++++++++++----
 1 files changed, 14 insertions(+), 4 deletions(-)

diffs (53 lines):

diff -r 81eb93907728 -r 5f958e204b08 sys/kern/vfs_cache.c
--- a/sys/kern/vfs_cache.c      Sun May 02 11:22:06 2004 +0000
+++ b/sys/kern/vfs_cache.c      Sun May 02 12:00:34 2004 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_cache.c,v 1.56 2004/04/25 16:42:41 simonb Exp $    */
+/*     $NetBSD: vfs_cache.c,v 1.57 2004/05/02 12:00:34 pk Exp $        */
 
 /*
  * Copyright (c) 1989, 1993
@@ -32,7 +32,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.56 2004/04/25 16:42:41 simonb Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.57 2004/05/02 12:00:34 pk Exp $");
 
 #include "opt_ddb.h"
 #include "opt_revcache.h"
@@ -133,7 +133,7 @@
 {
 
        pool_put(&namecache_pool, ncp);
-       numcache--; /* XXX MP */
+       numcache--;
 }
 
 static __inline struct namecache *
@@ -418,7 +418,6 @@
         * Free the cache slot at head of lru chain.
         */
        simple_lock(&namecache_slock);
-       KASSERT(cache_lookup_entry(dvp, cnp) == NULL);
        if (numcache < numvnodes) {
                numcache++;
                simple_unlock(&namecache_slock);
@@ -431,6 +430,17 @@
                simple_unlock(&namecache_slock);
                return;
        }
+
+       /*
+        * Concurrent lookups in the same directory may race for a
+        * cache entry. If we loose, free our tentative entry and return.
+        */
+       if (cache_lookup_entry(dvp, cnp) != NULL) {
+               cache_free(ncp);
+               simple_unlock(&namecache_slock);
+               return;
+       }
+
        /* Grab the vnode we just found. */
        ncp->nc_vp = vp;
        if (vp == NULL) {