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net: add CONFIG_PCPU_DEV_REFCNT

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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 <lkp@intel.com>

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-03-19 10:39:33 -07:00 committed by David S. Miller
parent 942f0c6e28
commit 919067cc84
3 changed files with 31 additions and 0 deletions
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13
include/linux/netdevice.h
View File

@ -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

8
net/Kconfig
View File

@ -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

10
net/core/dev.c
View File

@ -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 @@ free_all:
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;