[PATCH v2 net-next] net: add CONFIG_PCPU_DEV_REFCNT
From: Eric Dumazet <hidden>
Date: 2021-03-19 17:40:19
Subsystem:
networking drivers, networking [general], the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Eric Dumazet <edumazet@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 [off-list ref]
Signed-off-by: Eric Dumazet <edumazet@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