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>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index e490b84..3fb6fb6 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3817,14 +3817,7 @@ extern unsigned int      netdev_budget_usecs;
 /* Called by rtnetlink.c:rtnl_unlock() */
 void netdev_run_todo(void);
 
-/**
- *     dev_put - release reference to device
- *     @dev: network device
- *
- * Release reference to device to allow it to be freed.
- * Try using dev_put_track() instead.
- */
-static inline void dev_put(struct net_device *dev)
+static inline void __dev_put(struct net_device *dev)
 {
        if (dev) {
 #ifdef CONFIG_PCPU_DEV_REFCNT
@@ -3835,14 +3828,7 @@ static inline void dev_put(struct net_device *dev)
        }
 }
 
-/**
- *     dev_hold - get reference to device
- *     @dev: network device
- *
- * Hold reference to device to keep it from being freed.
- * Try using dev_hold_track() instead.
- */
-static inline void dev_hold(struct net_device *dev)
+static inline void __dev_hold(struct net_device *dev)
 {
        if (dev) {
 #ifdef CONFIG_PCPU_DEV_REFCNT
@@ -3853,11 +3839,24 @@ static inline void dev_hold(struct net_device *dev)
        }
 }
 
+static inline void __netdev_tracker_alloc(struct net_device *dev,
+                                         netdevice_tracker *tracker,
+                                         gfp_t gfp)
+{
+#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
+       ref_tracker_alloc(&dev->refcnt_tracker, tracker, gfp);
+#endif
+}
+
+/* netdev_tracker_alloc() can upgrade a prior untracked reference
+ * taken by dev_get_by_name()/dev_get_by_index() to a tracked one.
+ */
 static inline void netdev_tracker_alloc(struct net_device *dev,
                                        netdevice_tracker *tracker, gfp_t gfp)
 {
 #ifdef CONFIG_NET_DEV_REFCNT_TRACKER
-       ref_tracker_alloc(&dev->refcnt_tracker, tracker, gfp);
+       refcount_dec(&dev->refcnt_tracker.no_tracker);
+       __netdev_tracker_alloc(dev, tracker, gfp);
 #endif
 }
 
@@ -3873,8 +3872,8 @@ static inline void dev_hold_track(struct net_device *dev,
                                  netdevice_tracker *tracker, gfp_t gfp)
 {
        if (dev) {
-               dev_hold(dev);
-               netdev_tracker_alloc(dev, tracker, gfp);
+               __dev_hold(dev);
+               __netdev_tracker_alloc(dev, tracker, gfp);
        }
 }
 
@@ -3883,10 +3882,34 @@ static inline void dev_put_track(struct net_device *dev,
 {
        if (dev) {
                netdev_tracker_free(dev, tracker);
-               dev_put(dev);
+               __dev_put(dev);
        }
 }
 
+/**
+ *     dev_hold - get reference to device
+ *     @dev: network device
+ *
+ * Hold reference to device to keep it from being freed.
+ * Try using dev_hold_track() instead.
+ */
+static inline void dev_hold(struct net_device *dev)
+{
+       dev_hold_track(dev, NULL, GFP_ATOMIC);
+}
+
+/**
+ *     dev_put - release reference to device
+ *     @dev: network device
+ *
+ * Release reference to device to allow it to be freed.
+ * Try using dev_put_track() instead.
+ */
+static inline void dev_put(struct net_device *dev)
+{
+       dev_put_track(dev, NULL);
+}
+
 static inline void dev_replace_track(struct net_device *odev,
                                     struct net_device *ndev,
                                     netdevice_tracker *tracker,
@@ -3895,11 +3918,11 @@ static inline void dev_replace_track(struct net_device *odev,
        if (odev)
                netdev_tracker_free(odev, tracker);
 
-       dev_hold(ndev);
-       dev_put(odev);
+       __dev_hold(ndev);
+       __dev_put(odev);
 
        if (ndev)
-               netdev_tracker_alloc(ndev, tracker, gfp);
+               __netdev_tracker_alloc(ndev, tracker, gfp);
 }
 
 /* Carrier loss detection, dial on demand. The functions netif_carrier_on

diff --git a/net/core/dev.c b/net/core/dev.c
index f79744d..1eaa0b8 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10172,7 +10172,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
        dev->pcpu_refcnt = alloc_percpu(int);
        if (!dev->pcpu_refcnt)
                goto free_dev;
-       dev_hold(dev);
+       __dev_hold(dev);
 #else
        refcount_set(&dev->dev_refcnt, 1);
 #endif

diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index b0f5344..95098d1 100644 (file)
--- 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)