Commit 4c6c11ea authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8fd5522f

include/linux/netdevice.h

+46 −23
Original line number Diff line number Diff line
@@ -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);

	}

}
@@ -3883,8 +3882,32 @@ 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,
@@ -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

net/core/dev.c

+1 −1
Original line number Diff line number Diff line
@@ -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

net/core/link_watch.c

+3 −3
Original line number Diff line number Diff line
@@ -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)