ref_tracker: add a count of untracked references

We are still chasing a netdev refcount imbalance, and we suspect
we have one rogue dev_put() that is consuming a reference taken
from a dev_hold_track()

To detect this case, allow ref_tracker_alloc() and ref_tracker_free()
to be called with a NULL @trackerp parameter, and use a dedicated
refcount_t just for them.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ref_tracker.h

@@ -13,6 +13,7 @@ struct ref_tracker_dir {
 	spinlock_t		lock;
 	unsigned int		quarantine_avail;
 	refcount_t		untracked;
+	refcount_t		no_tracker;
 	bool			dead;
 	struct list_head	list; /* List of active trackers */
 	struct list_head	quarantine; /* List of dead trackers */
@@ -29,6 +30,7 @@ static inline void ref_tracker_dir_init(struct ref_tracker_dir *dir,
 	dir->quarantine_avail = quarantine_count;
 	dir->dead = false;
 	refcount_set(&dir->untracked, 1);
+	refcount_set(&dir->no_tracker, 1);
 	stack_depot_init();
 }
 

lib/ref_tracker.c

@@ -38,6 +38,7 @@ void ref_tracker_dir_exit(struct ref_tracker_dir *dir)
 	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);
 
@@ -75,6 +76,10 @@ int ref_tracker_alloc(struct ref_tracker_dir *dir,
 
 	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(sizeof(*tracker), gfp_mask);
@@ -98,13 +103,18 @@ int ref_tracker_free(struct ref_tracker_dir *dir,
 		     struct ref_tracker **trackerp)
 {
 	unsigned long entries[REF_TRACKER_STACK_ENTRIES];
-	struct ref_tracker *tracker = *trackerp;
 	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;