netdev - [PATCH v2 02/11] [DO NOT MERGE] ref_tracker: add a count of untracked references

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Message-Id: <20220221231705.1481059-5-andrzej.hajda@intel.com>
Date:   Tue, 22 Feb 2022 00:16:46 +0100
From:   Andrzej Hajda <andrzej.hajda@...el.com>
To:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, netdev <netdev@...r.kernel.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Chris Wilson <chris.p.wilson@...el.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: [PATCH v2 02/11] [DO NOT MERGE] ref_tracker: add a count of untracked references

From: Eric Dumazet <edumazet@...gle.com>

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@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Andrzej Hajda <andrzej.hajda@...el.com>
---
 include/linux/ref_tracker.h |  2 ++
 lib/ref_tracker.c           | 12 +++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/ref_tracker.h b/include/linux/ref_tracker.h
index a443abda937d8..9ca353ab712b5 100644
--- a/include/linux/ref_tracker.h
+++ b/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();
 }
 
diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
index 32ff6bd497f8e..9c0c2e09df666 100644
--- a/lib/ref_tracker.c
+++ b/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;
-- 
2.25.1