+ ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: ref_tracker: automatically register a file in debugfs for a ref_tracker_dir
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jeff Layton <jlayton@kernel.org>
Subject: ref_tracker: automatically register a file in debugfs for a ref_tracker_dir
Date: Tue, 03 Jun 2025 07:27:17 -0400

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.

Link: https://lkml.kernel.org/r/20250603-reftrack-dbgfs-v13-6-7b2a425019d8@kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Dumaze <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Krzysztof Karas <krzysztof.karas@intel.com>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Qasim Ijaz <qasdev00@gmail.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/ref_tracker.h |   23 +++++++++++
 lib/ref_tracker.c           |   67 ++++++++++++++++++++++++++++++++--
 2 files changed, 88 insertions(+), 2 deletions(-)

--- a/include/linux/ref_tracker.h~ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir
+++ a/include/linux/ref_tracker.h
@@ -20,12 +20,27 @@ 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
 
+#ifdef CONFIG_DEBUG_FS
+
+void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir);
+
+#else /* CONFIG_DEBUG_FS */
+
+static inline void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
+{
+}
+
+#endif /* CONFIG_DEBUG_FS */
+
 static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
 					unsigned int quarantine_count,
 					const char *class,
@@ -39,7 +54,11 @@ static inline void ref_tracker_dir_init(
 	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();
 }
 
@@ -68,6 +87,10 @@ static inline void ref_tracker_dir_init(
 {
 }
 
+static inline void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir)
+{
+}
+
 static inline void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
 {
 }
--- a/lib/ref_tracker.c~ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir
+++ a/lib/ref_tracker.c
@@ -29,6 +29,14 @@ 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)
 {
@@ -185,6 +193,7 @@ void ref_tracker_dir_exit(struct ref_tra
 	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);
@@ -312,8 +321,7 @@ static void __ostream_printf pr_ostream_
 	va_end(args);
 }
 
-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 = "",
@@ -327,6 +335,61 @@ ref_tracker_dir_seq_print(struct ref_tra
 	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);
+}
+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);
_

Patches currently in -mm which might be from jlayton@kernel.org are

ref_tracker-dont-use-%pk-in-pr_ostream-output.patch
ref_tracker-add-a-top-level-debugfs-directory-for-ref_tracker.patch
ref_tracker-have-callers-pass-output-function-to-pr_ostream.patch
ref_tracker-add-a-static-classname-string-to-each-ref_tracker_dir.patch
ref_tracker-allow-pr_ostream-to-print-directly-to-a-seq_file.patch
ref_tracker-automatically-register-a-file-in-debugfs-for-a-ref_tracker_dir.patch
ref_tracker-add-a-way-to-create-a-symlink-to-the-ref_tracker_dir-debugfs-file.patch
net-add-symlinks-to-ref_tracker_dir-for-netns.patch
ref_tracker-eliminate-the-ref_tracker_dir-name-field.patch