Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 533 insertions, 0 deletions

diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
new file mode 100644
index 000000000..30c999d57
--- /dev/null
+++ b/lib/ref_tracker.c
@@ -0,0 +1,533 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "ref_tracker: " fmt
+
+#include <linux/export.h>
+#include <linux/list_sort.h>
+#include <linux/ref_tracker.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+#include <linux/stackdepot.h>
+#include <linux/seq_file.h>
+
+#define REF_TRACKER_STACK_ENTRIES 16
+#define STACK_BUF_SIZE 1024
+
+struct ref_tracker {
+	struct list_head	head;   /* anchor into dir->list or dir->quarantine */
+	bool			dead;
+	depot_stack_handle_t	alloc_stack_handle;
+	depot_stack_handle_t	free_stack_handle;
+};
+
+struct ref_tracker_dir_stats {
+	int total;
+	int count;
+	struct {
+		depot_stack_handle_t stack_handle;
+		unsigned int count;
+	} stacks[];
+};
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/xarray.h>
+
+/*
+ * ref_tracker_dir_init() is usually called in allocation-safe contexts, but
+ * the same is not true of ref_tracker_dir_exit() which can be called from
+ * anywhere an object is freed. Removing debugfs dentries is a blocking
+ * operation, so we defer that work to the debugfs_reap_worker.
+ *
+ * Each dentry is tracked in the appropriate xarray.  When
+ * ref_tracker_dir_exit() is called, its entries in the xarrays are marked and
+ * the workqueue job is scheduled. The worker then runs and deletes any marked
+ * dentries asynchronously.
+ */
+static struct xarray		debugfs_dentries;
+static struct xarray		debugfs_symlinks;
+static struct work_struct	debugfs_reap_worker;
+
+#define REF_TRACKER_DIR_DEAD	XA_MARK_0
+static inline void ref_tracker_debugfs_mark(struct ref_tracker_dir *dir)
+{
+	unsigned long flags;
+
+	xa_lock_irqsave(&debugfs_dentries, flags);
+	__xa_set_mark(&debugfs_dentries, (unsigned long)dir, REF_TRACKER_DIR_DEAD);
+	xa_unlock_irqrestore(&debugfs_dentries, flags);
+
+	xa_lock_irqsave(&debugfs_symlinks, flags);
+	__xa_set_mark(&debugfs_symlinks, (unsigned long)dir, REF_TRACKER_DIR_DEAD);
+	xa_unlock_irqrestore(&debugfs_symlinks, flags);
+
+	schedule_work(&debugfs_reap_worker);
+}
+#else
+static inline void ref_tracker_debugfs_mark(struct ref_tracker_dir *dir)
+{
+}
+#endif
+
+static struct ref_tracker_dir_stats *
+ref_tracker_get_stats(struct ref_tracker_dir *dir, unsigned int limit)
+{
+	struct ref_tracker_dir_stats *stats;
+	struct ref_tracker *tracker;
+
+	stats = kmalloc_flex(*stats, stacks, limit, GFP_NOWAIT);
+	if (!stats)
+		return ERR_PTR(-ENOMEM);
+	stats->total = 0;
+	stats->count = 0;
+
+	list_for_each_entry(tracker, &dir->list, head) {
+		depot_stack_handle_t stack = tracker->alloc_stack_handle;
+		int i;
+
+		++stats->total;
+		for (i = 0; i < stats->count; ++i)
+			if (stats->stacks[i].stack_handle == stack)
+				break;
+		if (i >= limit)
+			continue;
+		if (i >= stats->count) {
+			stats->stacks[i].stack_handle = stack;
+			stats->stacks[i].count = 0;
+			++stats->count;
+		}
+		++stats->stacks[i].count;
+	}
+
+	return stats;
+}
+
+struct ostream {
+	void __ostream_printf (*func)(struct ostream *stream, char *fmt, ...);
+	char *prefix;
+	char *buf;
+	struct seq_file *seq;
+	int size, used;
+};
+
+static void __ostream_printf pr_ostream_log(struct ostream *stream, char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vprintk(fmt, args);
+	va_end(args);
+}
+
+static void __ostream_printf pr_ostream_buf(struct ostream *stream, char *fmt, ...)
+{
+	int ret, len = stream->size - stream->used;
+	va_list args;
+
+	va_start(args, fmt);
+	ret = vsnprintf(stream->buf + stream->used, len, fmt, args);
+	va_end(args);
+	if (ret > 0)
+		stream->used += min(ret, len);
+}
+
+#define pr_ostream(stream, fmt, args...) \
+({ \
+	struct ostream *_s = (stream); \
+\
+	_s->func(_s, fmt, ##args); \
+})
+
+static void
+__ref_tracker_dir_pr_ostream(struct ref_tracker_dir *dir,
+			     unsigned int display_limit, struct ostream *s)
+{
+	struct ref_tracker_dir_stats *stats;
+	unsigned int i = 0, skipped;
+	depot_stack_handle_t stack;
+	char *sbuf;
+
+	lockdep_assert_held(&dir->lock);
+
+	if (list_empty(&dir->list))
+		return;
+
+	stats = ref_tracker_get_stats(dir, display_limit);
+	if (IS_ERR(stats)) {
+		pr_ostream(s, "%s%s@%p: couldn't get stats, error %pe\n",
+			   s->prefix, dir->class, dir, stats);
+		return;
+	}
+
+	sbuf = kmalloc(STACK_BUF_SIZE, GFP_NOWAIT);
+
+	for (i = 0, skipped = stats->total; i < stats->count; ++i) {
+		stack = stats->stacks[i].stack_handle;
+		if (sbuf && !stack_depot_snprint(stack, sbuf, STACK_BUF_SIZE, 4))
+			sbuf[0] = 0;
+		pr_ostream(s, "%s%s@%p has %d/%d users at\n%s\n", s->prefix,
+			   dir->class, dir, stats->stacks[i].count,
+			   stats->total, sbuf);
+		skipped -= stats->stacks[i].count;
+	}
+
+	if (skipped)
+		pr_ostream(s, "%s%s@%p skipped reports about %d/%d users.\n",
+			   s->prefix, dir->class, dir, skipped, stats->total);
+
+	kfree(sbuf);
+
+	kfree(stats);
+}
+
+void ref_tracker_dir_print_locked(struct ref_tracker_dir *dir,
+				  unsigned int display_limit)
+{
+	struct ostream os = { .func = pr_ostream_log,
+			      .prefix = "ref_tracker: " };
+
+	__ref_tracker_dir_pr_ostream(dir, display_limit, &os);
+}
+EXPORT_SYMBOL(ref_tracker_dir_print_locked);
+
+void ref_tracker_dir_print(struct ref_tracker_dir *dir,
+			   unsigned int display_limit)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&dir->lock, flags);
+	ref_tracker_dir_print_locked(dir, display_limit);
+	spin_unlock_irqrestore(&dir->lock, flags);
+}
+EXPORT_SYMBOL(ref_tracker_dir_print);
+
+int ref_tracker_dir_snprint(struct ref_tracker_dir *dir, char *buf, size_t size)
+{
+	struct ostream os = { .func = pr_ostream_buf,
+			      .prefix = "ref_tracker: ",
+			      .buf = buf,
+			      .size = size };
+	unsigned long flags;
+
+	spin_lock_irqsave(&dir->lock, flags);
+	__ref_tracker_dir_pr_ostream(dir, 16, &os);
+	spin_unlock_irqrestore(&dir->lock, flags);
+
+	return os.used;
+}
+EXPORT_SYMBOL(ref_tracker_dir_snprint);
+
+void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
+{
+	struct ref_tracker *tracker, *n;
+	unsigned long flags;
+	bool leak = false;
+
+	dir->dead = true;
+	/*
+	 * The xarray entries must be marked before the dir->lock is taken to
+	 * protect simultaneous debugfs readers.
+	 */
+	ref_tracker_debugfs_mark(dir);
+	spin_lock_irqsave(&dir->lock, flags);
+	list_for_each_entry_safe(tracker, n, &dir->quarantine, head) {
+		list_del(&tracker->head);
+		kfree(tracker);
+		dir->quarantine_avail++;
+	}
+	if (!list_empty(&dir->list)) {
+		ref_tracker_dir_print_locked(dir, 16);
+		leak = true;
+		list_for_each_entry_safe(tracker, n, &dir->list, head) {
+			list_del(&tracker->head);
+			kfree(tracker);
+		}
+	}
+	spin_unlock_irqrestore(&dir->lock, flags);
+	WARN_ON_ONCE(leak);
+	WARN_ON_ONCE(refcount_read(&dir->untracked) != 1);
+	WARN_ON_ONCE(refcount_read(&dir->no_tracker) != 1);
+}
+EXPORT_SYMBOL(ref_tracker_dir_exit);
+
+int ref_tracker_alloc(struct ref_tracker_dir *dir,
+		      struct ref_tracker **trackerp,
+		      gfp_t gfp)
+{
+	unsigned long entries[REF_TRACKER_STACK_ENTRIES];
+	struct ref_tracker *tracker;
+	unsigned int nr_entries;
+	gfp_t gfp_mask = gfp | __GFP_NOWARN;
+	unsigned long flags;
+
+	WARN_ON_ONCE(dir->dead);
+
+	if (!trackerp) {
+		refcount_inc(&dir->no_tracker);
+		return 0;
+	}
+	if (gfp & __GFP_DIRECT_RECLAIM)
+		gfp_mask |= __GFP_NOFAIL;
+	*trackerp = tracker = kzalloc_obj(*tracker, gfp_mask);
+	if (unlikely(!tracker)) {
+		pr_err_once("memory allocation failure, unreliable refcount tracker.\n");
+		refcount_inc(&dir->untracked);
+		return -ENOMEM;
+	}
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
+	tracker->alloc_stack_handle = stack_depot_save(entries, nr_entries, gfp);
+
+	spin_lock_irqsave(&dir->lock, flags);
+	list_add(&tracker->head, &dir->list);
+	spin_unlock_irqrestore(&dir->lock, flags);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ref_tracker_alloc);
+
+int ref_tracker_free(struct ref_tracker_dir *dir,
+		     struct ref_tracker **trackerp)
+{
+	unsigned long entries[REF_TRACKER_STACK_ENTRIES];
+	depot_stack_handle_t stack_handle;
+	struct ref_tracker *tracker;
+	unsigned int nr_entries;
+	unsigned long flags;
+
+	WARN_ON_ONCE(dir->dead);
+
+	if (!trackerp) {
+		refcount_dec(&dir->no_tracker);
+		return 0;
+	}
+	tracker = *trackerp;
+	if (!tracker) {
+		refcount_dec(&dir->untracked);
+		return -EEXIST;
+	}
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
+	stack_handle = stack_depot_save(entries, nr_entries,
+					GFP_NOWAIT);
+
+	spin_lock_irqsave(&dir->lock, flags);
+	if (tracker->dead) {
+		pr_err("reference already released.\n");
+		if (tracker->alloc_stack_handle) {
+			pr_err("allocated in:\n");
+			stack_depot_print(tracker->alloc_stack_handle);
+		}
+		if (tracker->free_stack_handle) {
+			pr_err("freed in:\n");
+			stack_depot_print(tracker->free_stack_handle);
+		}
+		spin_unlock_irqrestore(&dir->lock, flags);
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+	tracker->dead = true;
+
+	tracker->free_stack_handle = stack_handle;
+
+	list_move_tail(&tracker->head, &dir->quarantine);
+	if (!dir->quarantine_avail) {
+		tracker = list_first_entry(&dir->quarantine, struct ref_tracker, head);
+		list_del(&tracker->head);
+	} else {
+		dir->quarantine_avail--;
+		tracker = NULL;
+	}
+	spin_unlock_irqrestore(&dir->lock, flags);
+
+	kfree(tracker);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ref_tracker_free);
+
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static struct dentry *ref_tracker_debug_dir = (struct dentry *)-ENOENT;
+
+static void __ostream_printf pr_ostream_seq(struct ostream *stream, char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	seq_vprintf(stream->seq, fmt, args);
+	va_end(args);
+}
+
+static int ref_tracker_dir_seq_print(struct ref_tracker_dir *dir, struct seq_file *seq)
+{
+	struct ostream os = { .func = pr_ostream_seq,
+			      .prefix = "",
+			      .seq = seq };
+
+	__ref_tracker_dir_pr_ostream(dir, 16, &os);
+
+	return os.used;
+}
+
+static int ref_tracker_debugfs_show(struct seq_file *f, void *v)
+{
+	struct ref_tracker_dir *dir = f->private;
+	unsigned long index = (unsigned long)dir;
+	unsigned long flags;
+	int ret;
+
+	/*
+	 * "dir" may not exist at this point if ref_tracker_dir_exit() has
+	 * already been called. Take care not to dereference it until its
+	 * legitimacy is established.
+	 *
+	 * The xa_lock is necessary to ensure that "dir" doesn't disappear
+	 * before its lock can be taken. If it's in the hash and not marked
+	 * dead, then it's safe to take dir->lock which prevents
+	 * ref_tracker_dir_exit() from completing. Once the dir->lock is
+	 * acquired, the xa_lock can be released. All of this must be IRQ-safe.
+	 */
+	xa_lock_irqsave(&debugfs_dentries, flags);
+	if (!xa_load(&debugfs_dentries, index) ||
+	    xa_get_mark(&debugfs_dentries, index, REF_TRACKER_DIR_DEAD)) {
+		xa_unlock_irqrestore(&debugfs_dentries, flags);
+		return -ENODATA;
+	}
+
+	spin_lock(&dir->lock);
+	xa_unlock(&debugfs_dentries);
+	ret = ref_tracker_dir_seq_print(dir, f);
+	spin_unlock_irqrestore(&dir->lock, flags);
+	return ret;
+}
+
+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];
+	struct dentry *dentry;
+	int ret;
+
+	/* No-op if already created */
+	dentry = xa_load(&debugfs_dentries, (unsigned long)dir);
+	if (dentry && !xa_is_err(dentry))
+		return;
+
+	ret = snprintf(name, sizeof(name), "%s@%p", dir->class, dir);
+	name[sizeof(name) - 1] = '\0';
+
+	if (ret < sizeof(name)) {
+		dentry = debugfs_create_file(name, S_IFREG | 0400,
+					     ref_tracker_debug_dir, dir,
+					     &ref_tracker_debugfs_fops);
+		if (!IS_ERR(dentry)) {
+			void *old;
+
+			old = xa_store_irq(&debugfs_dentries, (unsigned long)dir,
+					   dentry, GFP_KERNEL);
+
+			if (xa_is_err(old))
+				debugfs_remove(dentry);
+			else
+				WARN_ON_ONCE(old);
+		}
+	}
+}
+EXPORT_SYMBOL(ref_tracker_dir_debugfs);
+
+void __ostream_printf ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...)
+{
+	char name[NAME_MAX + 1];
+	struct dentry *symlink, *dentry;
+	va_list args;
+	int ret;
+
+	symlink = xa_load(&debugfs_symlinks, (unsigned long)dir);
+	dentry = xa_load(&debugfs_dentries, (unsigned long)dir);
+
+	/* Already created?*/
+	if (symlink && !xa_is_err(symlink))
+		return;
+
+	if (!dentry || xa_is_err(dentry))
+		return;
+
+	va_start(args, fmt);
+	ret = vsnprintf(name, sizeof(name), fmt, args);
+	va_end(args);
+	name[sizeof(name) - 1] = '\0';
+
+	if (ret < sizeof(name)) {
+		symlink = debugfs_create_symlink(name, ref_tracker_debug_dir,
+						 dentry->d_name.name);
+		if (!IS_ERR(symlink)) {
+			void *old;
+
+			old = xa_store_irq(&debugfs_symlinks, (unsigned long)dir,
+					   symlink, GFP_KERNEL);
+			if (xa_is_err(old))
+				debugfs_remove(symlink);
+			else
+				WARN_ON_ONCE(old);
+		}
+	}
+}
+EXPORT_SYMBOL(ref_tracker_dir_symlink);
+
+static void debugfs_reap_work(struct work_struct *work)
+{
+	struct dentry *dentry;
+	unsigned long index;
+	bool reaped;
+
+	do {
+		reaped = false;
+		xa_for_each_marked(&debugfs_symlinks, index, dentry, REF_TRACKER_DIR_DEAD) {
+			xa_erase_irq(&debugfs_symlinks, index);
+			debugfs_remove(dentry);
+			reaped = true;
+		}
+		xa_for_each_marked(&debugfs_dentries, index, dentry, REF_TRACKER_DIR_DEAD) {
+			xa_erase_irq(&debugfs_dentries, index);
+			debugfs_remove(dentry);
+			reaped = true;
+		}
+	} while (reaped);
+}
+
+static int __init ref_tracker_debugfs_postcore_init(void)
+{
+	INIT_WORK(&debugfs_reap_worker, debugfs_reap_work);
+	xa_init_flags(&debugfs_dentries, XA_FLAGS_LOCK_IRQ);
+	xa_init_flags(&debugfs_symlinks, XA_FLAGS_LOCK_IRQ);
+	return 0;
+}
+postcore_initcall(ref_tracker_debugfs_postcore_init);
+
+static int __init ref_tracker_debugfs_late_init(void)
+{
+	ref_tracker_debug_dir = debugfs_create_dir("ref_tracker", NULL);
+	return 0;
+}
+late_initcall(ref_tracker_debugfs_late_init);
+#endif /* CONFIG_DEBUG_FS */