Re: [PATCH v6 06/10] ref_tracker: automatically register a file in debugfs for a ref_tracker_dir

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 30 Apr 2025, Jeff Layton <jlayton@kernel.org> wrote:
> Currently, there is no convenient way to see the info that the
> ref_tracking infrastructure collects. Attempt to create a file in
> debugfs when called from ref_tracker_dir_init().
>
> The file is given the name "class@%px", as having the unmodified address
> is helpful for debugging. This should be safe since this directory is only
> accessible by root
>
> If debugfs file creation fails, a pr_warn will be isssued.
>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  include/linux/ref_tracker.h | 14 +++++++++
>  lib/ref_tracker.c           | 73 +++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 85 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
> index 2adae128d4b5e45f156af4775a1d184bb596fa91..c6e65d7ef4d4fc74c60fcabd19166c131d4173e2 100644
> --- a/include/linux/ref_tracker.h
> +++ b/include/linux/ref_tracker.h
> @@ -5,6 +5,7 @@
>  #include <linux/types.h>
>  #include <linux/spinlock.h>
>  #include <linux/stackdepot.h>
> +#include <linux/seq_file.h>

Nothing here requires seq_file.h as far as I can tell. Please avoid
superfluous header dependencies.

BR,
Jani.

>  
>  struct ref_tracker;
>  
> @@ -18,12 +19,17 @@ struct ref_tracker_dir {
>  	struct list_head	list; /* List of active trackers */
>  	struct list_head	quarantine; /* List of dead trackers */
>  	const char		*class; /* object classname */
> +#ifdef CONFIG_DEBUG_FS
> +	struct dentry		*dentry;
> +#endif
>  	char			name[32];
>  #endif
>  };
>  
>  #ifdef CONFIG_REF_TRACKER
>  
> +void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir);
> +
>  static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
>  					unsigned int quarantine_count,
>  					const char *class,
> @@ -37,7 +43,11 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
>  	refcount_set(&dir->untracked, 1);
>  	refcount_set(&dir->no_tracker, 1);
>  	dir->class = class;
> +#ifdef CONFIG_DEBUG_FS
> +	dir->dentry = NULL;
> +#endif
>  	strscpy(dir->name, name, sizeof(dir->name));
> +	ref_tracker_dir_debugfs(dir);
>  	stack_depot_init();
>  }
>  
> @@ -66,6 +76,10 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
>  {
>  }
>  
> +static inline void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
> +{
> +}
> +
>  static inline void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
>  {
>  }
> diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
> index b69c11e83c18c19aaa2dc23f802291d4a7e82a66..3ee4fd0f33407881cfa140dcb7d8b40e3c2722de 100644
> --- a/lib/ref_tracker.c
> +++ b/lib/ref_tracker.c
> @@ -31,6 +31,14 @@ struct ref_tracker_dir_stats {
>  	} stacks[];
>  };
>  
> +#ifdef CONFIG_DEBUG_FS
> +static void ref_tracker_debugfs_remove(struct ref_tracker_dir *dir);
> +#else
> +static inline void ref_tracker_debugfs_remove(struct ref_tracker_dir *dir)
> +{
> +}
> +#endif
> +
>  static struct ref_tracker_dir_stats *
>  ref_tracker_get_stats(struct ref_tracker_dir *dir, unsigned int limit)
>  {
> @@ -197,6 +205,7 @@ void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
>  	bool leak = false;
>  
>  	dir->dead = true;
> +	ref_tracker_debugfs_remove(dir);
>  	spin_lock_irqsave(&dir->lock, flags);
>  	list_for_each_entry_safe(tracker, n, &dir->quarantine, head) {
>  		list_del(&tracker->head);
> @@ -313,8 +322,7 @@ EXPORT_SYMBOL_GPL(ref_tracker_free);
>  #ifdef CONFIG_DEBUG_FS
>  #include <linux/debugfs.h>
>  
> -static __maybe_unused int
> -ref_tracker_dir_seq_print(struct ref_tracker_dir *dir, struct seq_file *seq)
> +static int ref_tracker_dir_seq_print(struct ref_tracker_dir *dir, struct seq_file *seq)
>  {
>  	struct ostream os = { .func = pr_ostream_seq,
>  			      .prefix = "",
> @@ -328,6 +336,67 @@ ref_tracker_dir_seq_print(struct ref_tracker_dir *dir, struct seq_file *seq)
>  	return os.used;
>  }
>  
> +static int ref_tracker_debugfs_show(struct seq_file *f, void *v)
> +{
> +	struct ref_tracker_dir *dir = f->private;
> +
> +	return ref_tracker_dir_seq_print(dir, f);
> +}
> +
> +static int ref_tracker_debugfs_open(struct inode *inode, struct file *filp)
> +{
> +	struct ref_tracker_dir *dir = inode->i_private;
> +
> +	return single_open(filp, ref_tracker_debugfs_show, dir);
> +}
> +
> +static const struct file_operations ref_tracker_debugfs_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= ref_tracker_debugfs_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= single_release,
> +};
> +
> +/**
> + * ref_tracker_dir_debugfs - create debugfs file for ref_tracker_dir
> + * @dir: ref_tracker_dir to be associated with debugfs file
> + *
> + * In most cases, a debugfs file will be created automatically for every
> + * ref_tracker_dir. If the object was created before debugfs is brought up
> + * then that may fail. In those cases, it is safe to call this at a later
> + * time to create the file.
> + */
> +void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
> +{
> +	char name[NAME_MAX + 1];
> +	int ret;
> +
> +	/* No-op if already created */
> +	if (!IS_ERR_OR_NULL(dir->dentry))
> +		return;
> +
> +	ret = snprintf(name, sizeof(name), "%s@%px", dir->class, dir);
> +	name[sizeof(name) - 1] = '\0';
> +
> +	if (ret < sizeof(name))
> +		dir->dentry = debugfs_create_file(name, S_IFREG | 0400,
> +						  ref_tracker_debug_dir, dir,
> +						  &ref_tracker_debugfs_fops);
> +	else
> +		dir->dentry = ERR_PTR(-ENAMETOOLONG);
> +
> +	if (IS_ERR(dir->dentry))
> +		pr_warn("ref_tracker: unable to create debugfs file for %s: %pe\n",
> +			name, dir->dentry);
> +}
> +EXPORT_SYMBOL(ref_tracker_dir_debugfs);
> +
> +static void ref_tracker_debugfs_remove(struct ref_tracker_dir *dir)
> +{
> +	debugfs_remove(dir->dentry);
> +}
> +
>  static int __init ref_tracker_debugfs_init(void)
>  {
>  	ref_tracker_debug_dir = debugfs_create_dir("ref_tracker", NULL);

-- 
Jani Nikula, Intel