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authorLouis Rilling <louis.rilling@kerlabs.com>2009-01-28 13:18:32 -0500
committerJoel Becker <joel.becker@oracle.com>2009-04-30 13:48:23 -0400
commite74cc06df3b05e2b2c1611a043f6e6dcadaab1eb (patch)
treec514c5f5149ce26ef9b44473bed18a7836540a38 /fs/configfs/dir.c
parent3c48f23adada870db612a0dd3488605c4af5c0a5 (diff)
configfs: Silence lockdep on mkdir() and rmdir()
When attaching default groups (subdirs) of a new group (in mkdir() or in configfs_register()), configfs recursively takes inode's mutexes along the path from the parent of the new group to the default subdirs. This is needed to ensure that the VFS will not race with operations on these sub-dirs. This is safe for the following reasons: - the VFS allows one to lock first an inode and second one of its children (The lock subclasses for this pattern are respectively I_MUTEX_PARENT and I_MUTEX_CHILD); - from this rule any inode path can be recursively locked in descending order as long as it stays under a single mountpoint and does not follow symlinks. Unfortunately lockdep does not know (yet?) how to handle such recursion. I've tried to use Peter Zijlstra's lock_set_subclass() helper to upgrade i_mutexes from I_MUTEX_CHILD to I_MUTEX_PARENT when we know that we might recursively lock some of their descendant, but this usage does not seem to fit the purpose of lock_set_subclass() because it leads to several i_mutex locked with subclass I_MUTEX_PARENT by the same task. >From inside configfs it is not possible to serialize those recursive locking with a top-level one, because mkdir() and rmdir() are already called with inodes locked by the VFS. So using some mutex_lock_nest_lock() is not an option. I am proposing two solutions: 1) one that wraps recursive mutex_lock()s with lockdep_off()/lockdep_on(). 2) (as suggested earlier by Peter Zijlstra) one that puts the i_mutexes recursively locked in different classes based on their depth from the top-level config_group created. This induces an arbitrary limit (MAX_LOCK_DEPTH - 2 == 46) on the nesting of configfs default groups whenever lockdep is activated but this limit looks reasonably high. Unfortunately, this also isolates VFS operations on configfs default groups from the others and thus lowers the chances to detect locking issues. Nobody likes solution 1), which I can understand. This patch implements solution 2). However lockdep is still not happy with configfs_depend_item(). Next patch reworks the locking of configfs_depend_item() and finally makes lockdep happy. [ Note: This hides a few locking interactions with the VFS from lockdep. That was my big concern, because we like lockdep's protection. However, the current state always dumps a spurious warning. The locking is correct, so I tell people to ignore the warning and that we'll keep our eyes on the locking to make sure it stays correct. With this patch, we eliminate the warning. We do lose some of the lockdep protections, but this only means that we still have to keep our eyes on the locking. We're going to do that anyway. -- Joel ] Signed-off-by: Louis Rilling <louis.rilling@kerlabs.com> Signed-off-by: Joel Becker <joel.becker@oracle.com>
Diffstat (limited to 'fs/configfs/dir.c')
-rw-r--r--fs/configfs/dir.c90
1 files changed, 90 insertions, 0 deletions
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 05373db21a4e..d4d871fba21e 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -78,6 +78,92 @@ static const struct dentry_operations configfs_dentry_ops = {
78 .d_delete = configfs_d_delete, 78 .d_delete = configfs_d_delete,
79}; 79};
80 80
81#ifdef CONFIG_LOCKDEP
82
83/*
84 * Helpers to make lockdep happy with our recursive locking of default groups'
85 * inodes (see configfs_attach_group() and configfs_detach_group()).
86 * We put default groups i_mutexes in separate classes according to their depth
87 * from the youngest non-default group ancestor.
88 *
89 * For a non-default group A having default groups A/B, A/C, and A/C/D, default
90 * groups A/B and A/C will have their inode's mutex in class
91 * default_group_class[0], and default group A/C/D will be in
92 * default_group_class[1].
93 *
94 * The lock classes are declared and assigned in inode.c, according to the
95 * s_depth value.
96 * The s_depth value is initialized to -1, adjusted to >= 0 when attaching
97 * default groups, and reset to -1 when all default groups are attached. During
98 * attachment, if configfs_create() sees s_depth > 0, the lock class of the new
99 * inode's mutex is set to default_group_class[s_depth - 1].
100 */
101
102static void configfs_init_dirent_depth(struct configfs_dirent *sd)
103{
104 sd->s_depth = -1;
105}
106
107static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
108 struct configfs_dirent *sd)
109{
110 int parent_depth = parent_sd->s_depth;
111
112 if (parent_depth >= 0)
113 sd->s_depth = parent_depth + 1;
114}
115
116static void
117configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
118{
119 /*
120 * item's i_mutex class is already setup, so s_depth is now only
121 * used to set new sub-directories s_depth, which is always done
122 * with item's i_mutex locked.
123 */
124 /*
125 * sd->s_depth == -1 iff we are a non default group.
126 * else (we are a default group) sd->s_depth > 0 (see
127 * create_dir()).
128 */
129 if (sd->s_depth == -1)
130 /*
131 * We are a non default group and we are going to create
132 * default groups.
133 */
134 sd->s_depth = 0;
135}
136
137static void
138configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
139{
140 /* We will not create default groups anymore. */
141 sd->s_depth = -1;
142}
143
144#else /* CONFIG_LOCKDEP */
145
146static void configfs_init_dirent_depth(struct configfs_dirent *sd)
147{
148}
149
150static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
151 struct configfs_dirent *sd)
152{
153}
154
155static void
156configfs_adjust_dir_dirent_depth_before_populate(struct configfs_dirent *sd)
157{
158}
159
160static void
161configfs_adjust_dir_dirent_depth_after_populate(struct configfs_dirent *sd)
162{
163}
164
165#endif /* CONFIG_LOCKDEP */
166
81/* 167/*
82 * Allocates a new configfs_dirent and links it to the parent configfs_dirent 168 * Allocates a new configfs_dirent and links it to the parent configfs_dirent
83 */ 169 */
@@ -94,6 +180,7 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare
94 INIT_LIST_HEAD(&sd->s_links); 180 INIT_LIST_HEAD(&sd->s_links);
95 INIT_LIST_HEAD(&sd->s_children); 181 INIT_LIST_HEAD(&sd->s_children);
96 sd->s_element = element; 182 sd->s_element = element;
183 configfs_init_dirent_depth(sd);
97 spin_lock(&configfs_dirent_lock); 184 spin_lock(&configfs_dirent_lock);
98 if (parent_sd->s_type & CONFIGFS_USET_DROPPING) { 185 if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
99 spin_unlock(&configfs_dirent_lock); 186 spin_unlock(&configfs_dirent_lock);
@@ -187,6 +274,7 @@ static int create_dir(struct config_item * k, struct dentry * p,
187 error = configfs_make_dirent(p->d_fsdata, d, k, mode, 274 error = configfs_make_dirent(p->d_fsdata, d, k, mode,
188 CONFIGFS_DIR | CONFIGFS_USET_CREATING); 275 CONFIGFS_DIR | CONFIGFS_USET_CREATING);
189 if (!error) { 276 if (!error) {
277 configfs_set_dir_dirent_depth(p->d_fsdata, d->d_fsdata);
190 error = configfs_create(d, mode, init_dir); 278 error = configfs_create(d, mode, init_dir);
191 if (!error) { 279 if (!error) {
192 inc_nlink(p->d_inode); 280 inc_nlink(p->d_inode);
@@ -789,11 +877,13 @@ static int configfs_attach_group(struct config_item *parent_item,
789 * error, as rmdir() would. 877 * error, as rmdir() would.
790 */ 878 */
791 mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD); 879 mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
880 configfs_adjust_dir_dirent_depth_before_populate(sd);
792 ret = populate_groups(to_config_group(item)); 881 ret = populate_groups(to_config_group(item));
793 if (ret) { 882 if (ret) {
794 configfs_detach_item(item); 883 configfs_detach_item(item);
795 dentry->d_inode->i_flags |= S_DEAD; 884 dentry->d_inode->i_flags |= S_DEAD;
796 } 885 }
886 configfs_adjust_dir_dirent_depth_after_populate(sd);
797 mutex_unlock(&dentry->d_inode->i_mutex); 887 mutex_unlock(&dentry->d_inode->i_mutex);
798 if (ret) 888 if (ret)
799 d_delete(dentry); 889 d_delete(dentry);