1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
|
From cacd95554dd49069967018ed94f37a46d98c6085 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Tue, 13 May 2014 13:09:15 +0200
Subject: [PATCH 09/14] ext2fs: use a seperate lock to protect nodehash
Previously, ext2fs used diskfs_node_refcnt_lock to serialize access to
the nodehash.
Use a separate lock to protect nodehash. Adjust the reference
counting accordingly. Every node in the nodehash carries a light
reference. When we are asked to give up that light reference, we
reacquire our lock momentarily to check whether someone else
reacquired a reference through the nodehash.
* ext2fs/inode.c (nodehash_lock): New lock.
(diskfs_cached_lookup): Use a separate lock to protect nodehash.
Adjust the reference counting accordingly.
(ifind): Likewise.
(diskfs_node_iterate): Likewise.
(diskfs_node_norefs): Move the code removing the node from nodehash...
(diskfs_try_dropping_softrefs): ... here, where we check whether
someone reacquired a reference, and if so hold on to our light
reference.
---
ext2fs/inode.c | 68 ++++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 50 insertions(+), 18 deletions(-)
diff --git a/ext2fs/inode.c b/ext2fs/inode.c
index ed78265..aa070a2 100644
--- a/ext2fs/inode.c
+++ b/ext2fs/inode.c
@@ -46,8 +46,18 @@
#define INOHASH(ino) (((unsigned)(ino))%INOHSZ)
#endif
+/* The nodehash is a cache of nodes.
+
+ Access to nodehash and nodehash_nr_items is protected by
+ nodehash_lock.
+
+ Every node in the nodehash carries a light reference. When we are
+ asked to give up that light reference, we reacquire our lock
+ momentarily to check whether someone else reacquired a reference
+ through the nodehash. */
static struct node *nodehash[INOHSZ];
static size_t nodehash_nr_items;
+static pthread_mutex_t nodehash_lock = PTHREAD_MUTEX_INITIALIZER;
static error_t read_node (struct node *np);
@@ -71,12 +81,12 @@ diskfs_cached_lookup (ino_t inum, struct node **npp)
struct node *np;
struct disknode *dn;
- pthread_spin_lock (&diskfs_node_refcnt_lock);
+ pthread_mutex_lock (&nodehash_lock);
for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext)
if (np->cache_id == inum)
{
- np->references++;
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ diskfs_nref (np);
+ pthread_mutex_unlock (&nodehash_lock);
pthread_mutex_lock (&np->lock);
*npp = np;
return 0;
@@ -86,7 +96,7 @@ diskfs_cached_lookup (ino_t inum, struct node **npp)
dn = malloc (sizeof (struct disknode));
if (! dn)
{
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ pthread_mutex_unlock (&nodehash_lock);
return ENOMEM;
}
dn->dirents = 0;
@@ -107,9 +117,10 @@ diskfs_cached_lookup (ino_t inum, struct node **npp)
dn->hnext->dn->hprevp = &dn->hnext;
dn->hprevp = &nodehash[INOHASH(inum)];
nodehash[INOHASH(inum)] = np;
+ diskfs_nref_light (np);
nodehash_nr_items += 1;
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ pthread_mutex_unlock (&nodehash_lock);
/* Get the contents of NP off disk. */
err = read_node (np);
@@ -140,14 +151,13 @@ ifind (ino_t inum)
{
struct node *np;
- pthread_spin_lock (&diskfs_node_refcnt_lock);
+ pthread_mutex_lock (&nodehash_lock);
for (np = nodehash[INOHASH(inum)]; np; np = np->dn->hnext)
{
if (np->cache_id != inum)
continue;
- assert (np->references);
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ pthread_mutex_unlock (&nodehash_lock);
return np;
}
assert (0);
@@ -158,11 +168,6 @@ ifind (ino_t inum)
void
diskfs_node_norefs (struct node *np)
{
- *np->dn->hprevp = np->dn->hnext;
- if (np->dn->hnext)
- np->dn->hnext->dn->hprevp = np->dn->hprevp;
- nodehash_nr_items -= 1;
-
if (np->dn->dirents)
free (np->dn->dirents);
assert (!np->dn->pager);
@@ -180,6 +185,33 @@ diskfs_node_norefs (struct node *np)
void
diskfs_try_dropping_softrefs (struct node *np)
{
+ pthread_mutex_lock (&nodehash_lock);
+ if (np->dn->hnext != NULL)
+ {
+ /* Check if someone reacquired a reference through the
+ nodehash. */
+ unsigned int references;
+ pthread_spin_lock (&diskfs_node_refcnt_lock);
+ references = np->references;
+ pthread_spin_unlock (&diskfs_node_refcnt_lock);
+
+ if (references > 0)
+ {
+ /* A reference was reacquired through a hash table lookup.
+ It's fine, we didn't touch anything yet. */
+ pthread_mutex_unlock (&nodehash_lock);
+ return;
+ }
+
+ *np->dn->hprevp = np->dn->hnext;
+ if (np->dn->hnext)
+ np->dn->hnext->dn->hprevp = np->dn->hprevp;
+ np->dn->hnext = NULL;
+ nodehash_nr_items -= 1;
+ diskfs_nrele_light (np);
+ }
+ pthread_mutex_unlock (&nodehash_lock);
+
drop_pager_softrefs (np);
}
@@ -556,12 +588,12 @@ diskfs_node_iterate (error_t (*fun)(struct node *))
size_t num_nodes;
struct node *node, **node_list, **p;
- pthread_spin_lock (&diskfs_node_refcnt_lock);
+ pthread_mutex_lock (&nodehash_lock);
/* We must copy everything from the hash table into another data structure
to avoid running into any problems with the hash-table being modified
during processing (normally we delegate access to hash-table with
- diskfs_node_refcnt_lock, but we can't hold this while locking the
+ nodehash_lock, but we can't hold this while locking the
individual node locks). */
num_nodes = nodehash_nr_items;
@@ -570,7 +602,7 @@ diskfs_node_iterate (error_t (*fun)(struct node *))
node_list = malloc (num_nodes * sizeof (struct node *));
if (node_list == NULL)
{
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ pthread_mutex_unlock (&nodehash_lock);
ext2_debug ("unable to allocate temporary node table");
return ENOMEM;
}
@@ -580,10 +612,10 @@ diskfs_node_iterate (error_t (*fun)(struct node *))
for (node = nodehash[n]; node; node = node->dn->hnext)
{
*p++ = node;
- node->references++;
+ diskfs_nref (node);
}
- pthread_spin_unlock (&diskfs_node_refcnt_lock);
+ pthread_mutex_unlock (&nodehash_lock);
p = node_list;
while (num_nodes-- > 0)
--
2.0.0.rc2
|
