net: refine dev_put()/dev_hold() debugging

We are still chasing some syzbot reports where we think a rogue dev_put()
is called with no corresponding prior dev_hold().
Unfortunately it eats a reference on dev->dev_refcnt taken by innocent
dev_hold_track(), meaning that the refcount saturation splat comes
too late to be useful.

Make sure that 'not tracked' dev_put() and dev_hold() better use
CONFIG_NET_DEV_REFCNT_TRACKER=y debug infrastructure:

Prior patch in the series allowed ref_tracker_alloc() and ref_tracker_free()
to be called with a NULL @trackerp parameter, and to use a separate refcount
only to detect too many put() even in the following case:

dev_hold_track(dev, tracker_1, GFP_ATOMIC);
 dev_hold(dev);
 dev_put(dev);
 dev_put(dev); // Should complain loudly here.
dev_put_track(dev, tracker_1); // instead of here

Add clarification about netdev_tracker_alloc() role.

v2: I replaced the dev_put() in linkwatch_do_dev()
    with __dev_put() because callers called netdev_tracker_free().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index b0f5344d1185..95098d1a49bd 100644
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -166,10 +166,10 @@ static void linkwatch_do_dev(struct net_device *dev)
 
 		netdev_state_change(dev);
 	}
-	/* Note: our callers are responsible for
-	 * calling netdev_tracker_free().
+	/* Note: our callers are responsible for calling netdev_tracker_free().
+	 * This is the reason we use __dev_put() instead of dev_put().
 	 */
-	dev_put(dev);
+	__dev_put(dev);
 }
 
 static void __linkwatch_run_queue(int urgent_only)