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net: refine dev_put()/dev_hold() debugging

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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>
This commit is contained in:
Eric Dumazet
2022-02-04 14:42:37 -08:00
committed by David S. Miller
parent 8fd5522f44
commit 4c6c11ea0f
3 changed files with 50 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

69
include/linux/netdevice.h
View File

@@ -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

2
net/core/dev.c
View File

@@ -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

6
net/core/link_watch.c
View File

@@ -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)