When creating a config_group (resp. registering a subsystem) with nested default
groups, lockdep raises a warning since it sees a lock recursion of class
I_MUTEX_CHILD in populate_groups().

This patch makes such default groups creations lockdep-friendly by increasing
the i_mutex sub-class from I_MUTEX_CHILD onwards when descending the default
groups tree.

With this patch the depth of default group trees is limited to
MAX_LOCKDEP_SUBCLASSES - I_MUTEX_CHILD - 1 == 3. This limit is removed when not
compiling lockdep.

Signed-off-by: Louis Rilling
---
fs/configfs/configfs_internal.h | 3 +
fs/configfs/dir.c | 61 ++++++++++++++++++++++++++++++++++------
fs/configfs/mount.c | 3 +
3 files changed, 59 insertions(+), 8 deletions(-)



Index: b/fs/configfs/configfs_internal.h
================================================== =================
--- a/fs/configfs/configfs_internal.h 2008-05-21 09:40:25.000000000 +0200
+++ b/fs/configfs/configfs_internal.h 2008-05-22 12:38:02.000000000 +0200
@@ -38,6 +38,9 @@ struct configfs_dirent {
umode_t s_mode;
struct dentry * s_dentry;
struct iattr * s_iattr;
+#ifdef CONFIG_LOCKDEP
+ int s_lock_level;
+#endif
};

#define CONFIGFS_ROOT 0x0001
Index: b/fs/configfs/dir.c
================================================== =================
--- a/fs/configfs/dir.c 2008-05-21 09:40:25.000000000 +0200
+++ b/fs/configfs/dir.c 2008-05-22 12:59:23.000000000 +0200
@@ -36,6 +36,37 @@

DECLARE_RWSEM(configfs_rename_sem);

+#ifdef CONFIG_LOCKDEP
+static inline int set_dirent_lock_level(struct configfs_dirent *prev_sd,
+ struct configfs_dirent *sd)
+{
+ int lock_level = prev_sd->s_lock_level + 1;
+ if (lock_level + I_MUTEX_CHILD < MAX_LOCKDEP_SUBCLASSES) {
+ sd->s_lock_level = lock_level;
+ return lock_level;
+ }
+ sd->s_lock_level = -1;
+ return -ELOOP;
+}
+
+static inline void reset_dirent_lock_level(struct configfs_dirent *sd)
+{
+ sd->s_lock_level = -1;
+}
+
+#else /* CONFIG_LOCKDEP */
+
+static inline int set_dirent_lock_level(struct configfs_dirent *prev_sd,
+ struct configfs_dirent *sd)
+{
+ return 0;
+}
+
+static inline void reset_dirent_lock_level(struct configfs_dirent *sd)
+{
+}
+#endif /* CONFIG_LOCKDEP */
+
static void configfs_d_iput(struct dentry * dentry,
struct inode * inode)
{
@@ -533,6 +564,10 @@ static int populate_groups(struct config
{
struct config_group *new_group;
struct dentry *dentry = group->cg_item.ci_dentry;
+ struct configfs_dirent *sd = dentry->d_fsdata;
+ struct configfs_dirent *parent_sd =
+ group->cg_item.ci_parent->ci_dentry->d_fsdata;
+ int lock_level;
int ret = 0;
int i;

@@ -546,17 +581,27 @@ static int populate_groups(struct config
* That said, taking our i_mutex is closer to mkdir
* emulation, and shouldn't hurt.
*/
- mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
+ /* lock_level starts at zero for the non default group */
+ lock_level = set_dirent_lock_level(parent_sd, sd);
+ if (lock_level < 0) {
+ /* Too deeply nested default groups */
+ ret = lock_level;
+ } else {
+ mutex_lock_nested(&dentry->d_inode->i_mutex,
+ I_MUTEX_CHILD + lock_level);

- for (i = 0; group->default_groups[i]; i++) {
- new_group = group->default_groups[i];
+ for (i = 0; group->default_groups[i]; i++) {
+ new_group = group->default_groups[i];

- ret = create_default_group(group, new_group);
- if (ret)
- break;
- }
+ ret = create_default_group(group, new_group);
+ if (ret)
+ break;
+ }

- mutex_unlock(&dentry->d_inode->i_mutex);
+ mutex_unlock(&dentry->d_inode->i_mutex);
+ /* Reset for future sub-group creations */
+ reset_dirent_lock_level(sd);
+ }
}

if (ret)
Index: b/fs/configfs/mount.c
================================================== =================
--- a/fs/configfs/mount.c 2008-05-21 09:40:25.000000000 +0200
+++ b/fs/configfs/mount.c 2008-05-22 12:38:02.000000000 +0200
@@ -64,6 +64,9 @@ static struct configfs_dirent configfs_r
.s_element = &configfs_root_group.cg_item,
.s_type = CONFIGFS_ROOT,
.s_iattr = NULL,
+#ifdef CONFIG_LOCKDEP
+ .s_lock_level = -1,
+#endif
};

static int configfs_fill_super(struct super_block *sb, void *data, int silent)

--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes

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