On Thu, Dec 18, 2008 at 07:00:17PM +0100, Louis Rilling wrote:
> >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), what I can understand.

Me too :-P

> 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.

<snip>

> #define CONFIGFS_ROOT 0x0001
> diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
> index 8e93341..f21be74 100644
> --- a/fs/configfs/dir.c
> +++ b/fs/configfs/dir.c
> @@ -94,6 +94,9 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare
> INIT_LIST_HEAD(&sd->s_links);
> INIT_LIST_HEAD(&sd->s_children);
> sd->s_element = element;
> +#ifdef CONFIG_LOCKDEP
> + sd->s_depth = -1;
> +#endif
> spin_lock(&configfs_dirent_lock);
> if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
> spin_unlock(&configfs_dirent_lock);
> @@ -176,6 +179,17 @@ static int init_symlink(struct inode * inode)
> return 0;
> }
>
> +#ifdef CONFIG_LOCKDEP
> +static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
> + struct configfs_dirent *sd)
> +{
> + int parent_depth = parent_sd->s_depth;
> +
> + if (parent_depth >= 0)
> + sd->s_depth = parent_depth + 1;
> +}
> +#endif
> +
> static int create_dir(struct config_item * k, struct dentry * p,
> struct dentry * d)
> {
> @@ -187,6 +201,9 @@ static int create_dir(struct config_item * k, struct dentry * p,
> error = configfs_make_dirent(p->d_fsdata, d, k, mode,
> CONFIGFS_DIR | CONFIGFS_USET_CREATING);
> if (!error) {
> +#ifdef CONFIG_LOCKDEP
> + configfs_set_dir_dirent_depth(p->d_fsdata, d->d_fsdata);
> +#endif
> error = configfs_create(d, mode, init_dir);
> if (!error) {
> inc_nlink(p->d_inode);

Can you change this to provide non-lockdep versions of
functions? We don't want "#ifdef CONFIG_LOCKDEP" everywhere. What we
want is the code to call functions unconditionally, and the functions to
do nothing if lockdep is not enabled. Like:

#ifdef CONFIG_LOCKDEP
static inline void configfs_init_dir_dirent_depth(dirent)
{
dirent->s_depth = -1;
}

static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
struct configfs_dirent *sd)
{
int parent_depth = parent_sd->s_depth;

if (parent_depth >= 0)
sd->s_depth = parent_depth + 1;
}
#else
static inline void configfs_init_dir_dirent_depth(dirent)
{
}

static void configfs_set_dir_dirent_depth(struct configfs_dirent *parent_sd,
struct configfs_dirent *sd)
{
}
#endif

This makes the callsites much nicer to read:

@@ -94,6 +94,9 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare
INIT_LIST_HEAD(&sd->s_links);
INIT_LIST_HEAD(&sd->s_children);
sd->s_element = element;
+ configfs_init_dir_dirent_depth(sd);
spin_lock(&configfs_dirent_lock);
if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {
spin_unlock(&configfs_dirent_lock);
@@ -187,6 +201,7 @@ static int create_dir(struct config_item * k, struct dentry * p,
error = configfs_make_dirent(p->d_fsdata, d, k, mode,
CONFIGFS_DIR | CONFIGFS_USET_CREATING);
if (!error) {
+ configfs_set_dir_dirent_depth(p->d_fsdata, d->d_fsdata);
error = configfs_create(d, mode, init_dir);
if (!error) {
inc_nlink(p->d_inode);

Otherwise, this patch seems pretty straightforward.

Joel

--

Life's Little Instruction Book #30

"Never buy a house without a fireplace."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127