From: Eric Dumazet <eduma...@google.com>
I was working on a syzbot issue, claiming one device could not be
dismantled because its refcount was -1
unregister_netdevice: waiting for sit0 to become free. Usage count = -1
It would be nice if syzbot could trigger a warning at the time
this reference count became negative.
This patch adds CONFIG_PCPU_DEV_REFCNT options which defaults
to per cpu variables (as before this patch) on SMP builds.
v2: free_dev label in alloc_netdev_mqs() is moved to avoid
a compiler warning (-Wunused-label), as reported
by kernel test robot <l...@intel.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
---
include/linux/netdevice.h | 13 +++++++++++++
net/Kconfig | 8 ++++++++
net/core/dev.c | 10 ++++++++++
3 files changed, 31 insertions(+)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index
4940509999beeb93ca4ad214e65d68e622a484cb..8f003955c485b81210ed56f7e1c24080b4bb46eb
100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2092,7 +2092,12 @@ struct net_device {
u32 proto_down_reason;
struct list_head todo_list;
+
+#ifdef CONFIG_PCPU_DEV_REFCNT
int __percpu *pcpu_refcnt;
+#else
+ refcount_t dev_refcnt;
+#endif
struct list_head link_watch_list;
@@ -4044,7 +4049,11 @@ void netdev_run_todo(void);
*/
static inline void dev_put(struct net_device *dev)
{
+#ifdef CONFIG_PCPU_DEV_REFCNT
this_cpu_dec(*dev->pcpu_refcnt);
+#else
+ refcount_dec(&dev->dev_refcnt);
+#endif
}
/**
@@ -4055,7 +4064,11 @@ static inline void dev_put(struct net_device *dev)
*/
static inline void dev_hold(struct net_device *dev)
{
+#ifdef CONFIG_PCPU_DEV_REFCNT
this_cpu_inc(*dev->pcpu_refcnt);
+#else
+ refcount_inc(&dev->dev_refcnt);
+#endif
}
/* Carrier loss detection, dial on demand. The functions netif_carrier_on
diff --git a/net/Kconfig b/net/Kconfig
index
0ead7ec0d2bd9ccbbfeab32f1892a9afd2a3eb77..9c456acc379e78caa9e45d4f1335802a05663a0f
100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -245,6 +245,14 @@ source "net/l3mdev/Kconfig"
source "net/qrtr/Kconfig"
source "net/ncsi/Kconfig"
+config PCPU_DEV_REFCNT
+ bool "Use percpu variables to maintain network device refcount"
+ depends on SMP
+ default y
+ help
+ network device refcount are using per cpu variables if this option is
set.
+ This can be forced to N to detect underflows (with a performance
drop).
+
config RPS
bool
depends on SMP && SYSFS
diff --git a/net/core/dev.c b/net/core/dev.c
index
4961fc2e9b1967c0d63b53cd809d52b43be0ed4b..be941ed754ac71d0839604bcfdd8ab67c339d27f
100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10312,11 +10312,15 @@ EXPORT_SYMBOL(register_netdev);
int netdev_refcnt_read(const struct net_device *dev)
{
+#ifdef CONFIG_PCPU_DEV_REFCNT
int i, refcnt = 0;
for_each_possible_cpu(i)
refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);
return refcnt;
+#else
+ return refcount_read(&dev->dev_refcnt);
+#endif
}
EXPORT_SYMBOL(netdev_refcnt_read);
@@ -10674,9 +10678,11 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv,
const char *name,
dev = PTR_ALIGN(p, NETDEV_ALIGN);
dev->padded = (char *)dev - (char *)p;
+#ifdef CONFIG_PCPU_DEV_REFCNT
dev->pcpu_refcnt = alloc_percpu(int);
if (!dev->pcpu_refcnt)
goto free_dev;
+#endif
if (dev_addr_init(dev))
goto free_pcpu;
@@ -10740,8 +10746,10 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv,
const char *name,
return NULL;
free_pcpu:
+#ifdef CONFIG_PCPU_DEV_REFCNT
free_percpu(dev->pcpu_refcnt);
free_dev:
+#endif
netdev_freemem(dev);
return NULL;
}
@@ -10783,8 +10791,10 @@ void free_netdev(struct net_device *dev)
list_for_each_entry_safe(p, n, &dev->napi_list, dev_list)
netif_napi_del(p);
+#ifdef CONFIG_PCPU_DEV_REFCNT
free_percpu(dev->pcpu_refcnt);
dev->pcpu_refcnt = NULL;
+#endif
free_percpu(dev->xdp_bulkq);
dev->xdp_bulkq = NULL;
--
2.31.0.291.g576ba9dcdaf-goog
