Module Name: src
Committed By: ad
Date: Mon Mar 23 18:37:31 UTC 2020
Modified Files:
src/sys/kern: vfs_cache.c
Log Message:
Fix a race between cache_enter() and cache_lookup(). Make sure the cache
entry is fully constructed before it appears on a vnode list.
To generate a diff of this commit:
cvs rdiff -u -r1.129 -r1.130 src/sys/kern/vfs_cache.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/vfs_cache.c
diff -u src/sys/kern/vfs_cache.c:1.129 src/sys/kern/vfs_cache.c:1.130
--- src/sys/kern/vfs_cache.c:1.129 Mon Mar 23 18:33:43 2020
+++ src/sys/kern/vfs_cache.c Mon Mar 23 18:37:30 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: vfs_cache.c,v 1.129 2020/03/23 18:33:43 ad Exp $ */
+/* $NetBSD: vfs_cache.c,v 1.130 2020/03/23 18:37:30 ad Exp $ */
/*-
* Copyright (c) 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -172,7 +172,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.129 2020/03/23 18:33:43 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_cache.c,v 1.130 2020/03/23 18:37:30 ad Exp $");
#define __NAMECACHE_PRIVATE
#ifdef _KERNEL_OPT
@@ -896,16 +896,20 @@ cache_enter(struct vnode *dvp, struct vn
ncp = kmem_alloc(sz, KM_SLEEP);
}
- /* Fill in cache info. */
+ /*
+ * Fill in cache info. For negative hits, save the ISWHITEOUT flag
+ * so we can restore it later when the cache entry is used again.
+ */
+ ncp->nc_vp = vp;
ncp->nc_dvp = dvp;
ncp->nc_key = cache_key(name, namelen);
ncp->nc_nlen = namelen;
+ ncp->nc_whiteout = ((cnflags & ISWHITEOUT) != 0);
memcpy(ncp->nc_name, name, namelen);
/*
- * Insert to the directory. Concurrent lookups in the same
- * directory may race for a cache entry. There can also be hash
- * value collisions. If there's a entry there already, purge it.
+ * Insert to the directory. Concurrent lookups may race for a cache
+ * entry. If there's a entry there already, purge it.
*/
rw_enter(&dvi->vi_nc_lock, RW_WRITER);
oncp = rb_tree_insert_node(&dvi->vi_nc_tree, ncp);
@@ -920,16 +924,23 @@ cache_enter(struct vnode *dvp, struct vn
KASSERT(oncp == ncp);
}
- /* Then insert to the vnode. */
- if (vp == NULL) {
- /*
- * For negative hits, save the ISWHITEOUT flag so we can
- * restore it later when the cache entry is used again.
- */
- ncp->nc_vp = NULL;
- ncp->nc_whiteout = ((cnflags & ISWHITEOUT) != 0);
- } else {
- /* Partially sort the per-vnode list: dots go to back. */
+ /*
+ * With the directory lock still held, insert to the tail of the
+ * ACTIVE LRU list (new) and with the LRU lock held take the to
+ * opportunity to incrementally balance the lists.
+ */
+ mutex_enter(&cache_lru_lock);
+ ncp->nc_lrulist = LRU_ACTIVE;
+ cache_lru.count[LRU_ACTIVE]++;
+ TAILQ_INSERT_TAIL(&cache_lru.list[LRU_ACTIVE], ncp, nc_lru);
+ cache_deactivate();
+ mutex_exit(&cache_lru_lock);
+
+ /*
+ * Finally, insert to the vnode, and unlock. Partially sort the
+ * per-vnode list: dots go to back.
+ */
+ if (vp != NULL) {
vnode_impl_t *vi = VNODE_TO_VIMPL(vp);
rw_enter(&vi->vi_nc_listlock, RW_WRITER);
if ((namelen == 1 && name[0] == '.') ||
@@ -939,21 +950,7 @@ cache_enter(struct vnode *dvp, struct vn
TAILQ_INSERT_HEAD(&vi->vi_nc_list, ncp, nc_list);
}
rw_exit(&vi->vi_nc_listlock);
- ncp->nc_vp = vp;
- ncp->nc_whiteout = false;
}
-
- /*
- * Finally, insert to the tail of the ACTIVE LRU list (new) and
- * with the LRU lock held take the to opportunity to incrementally
- * balance the lists.
- */
- mutex_enter(&cache_lru_lock);
- ncp->nc_lrulist = LRU_ACTIVE;
- cache_lru.count[LRU_ACTIVE]++;
- TAILQ_INSERT_TAIL(&cache_lru.list[LRU_ACTIVE], ncp, nc_lru);
- cache_deactivate();
- mutex_exit(&cache_lru_lock);
rw_exit(&dvi->vi_nc_lock);
}
