[PATCH 7/8] netpoll: fix initialization/NAPI race

Matt Mackall
2005-08-12T02:19:46Z

This fixes a race during initialization with the NAPI softirq
processing by using an RCU approach.

This race was discovered when refill_skbs() was added to
the setup code.

Signed-off-by: Matt Mackall <mpm@selenic.com>

Index: l/net/core/netpoll.c
===================================================================
--- l.orig/net/core/netpoll.c 2005-08-09 00:56:23.000000000 -0500
+++ l/net/core/netpoll.c 2005-08-11 01:50:24.000000000 -0500
@@ -731,6 +731,9 @@ int netpoll_setup(struct netpoll *np)
/* last thing to do is link it to the net device structure */
ndev->npinfo = npinfo;

+ /* avoid racing with NAPI reading npinfo */
+ synchronize_rcu();
+
return 0;

release:
Index: l/include/linux/netpoll.h
===================================================================
--- l.orig/include/linux/netpoll.h 2005-08-09 00:56:23.000000000 -0500
+++ l/include/linux/netpoll.h 2005-08-11 01:33:42.000000000 -0500
@@ -9,6 +9,7 @@

#include <linux/netdevice.h>
#include <linux/interrupt.h>
+#include <linux/rcupdate.h>
#include <linux/list.h>

struct netpoll;
@@ -61,25 +62,31 @@ static inline int netpoll_rx(struct sk_b
return ret;
}

-static inline void netpoll_poll_lock(struct net_device *dev)
+static inline void *netpoll_poll_lock(struct net_device *dev)
{
+ rcu_read_lock(); /* deal with race on ->npinfo */
if (dev->npinfo) {
spin_lock(&dev->npinfo->poll_lock);
dev->npinfo->poll_owner = smp_processor_id();
+ return dev->npinfo;
}
+ return NULL;
}

-static inline void netpoll_poll_unlock(struct net_device *dev)
+static inline void netpoll_poll_unlock(void *have)
{
- if (dev->npinfo) {
- dev->npinfo->poll_owner = -1;
- spin_unlock(&dev->npinfo->poll_lock);
+ struct netpoll_info *npi = have;
+
+ if (npi) {
+ npi->poll_owner = -1;
+ spin_unlock(&npi->poll_lock);
}
+ rcu_read_unlock();
}

#else
#define netpoll_rx(a) 0
-#define netpoll_poll_lock(a)
+#define netpoll_poll_lock(a) 0
#define netpoll_poll_unlock(a)
#endif

Index: l/net/core/dev.c
===================================================================
--- l.orig/net/core/dev.c 2005-08-09 00:56:23.000000000 -0500
+++ l/net/core/dev.c 2005-08-11 01:34:08.000000000 -0500
@@ -1696,7 +1696,8 @@ static void net_rx_action(struct softirq
struct softnet_data *queue = &__get_cpu_var(softnet_data);
unsigned long start_time = jiffies;
int budget = netdev_budget;
-
+ void *have;
+
local_irq_disable();

while (!list_empty(&queue->poll_list)) {
@@ -1709,10 +1710,10 @@ static void net_rx_action(struct softirq

dev = list_entry(queue->poll_list.next,
struct net_device, poll_list);
- netpoll_poll_lock(dev);
+ have = netpoll_poll_lock(dev);

if (dev->quota <= 0 || dev->poll(dev, &budget)) {
- netpoll_poll_unlock(dev);
+ netpoll_poll_unlock(have);
local_irq_disable();
list_del(&dev->poll_list);
list_add_tail(&dev->poll_list, &queue->poll_list);
@@ -1721,7 +1722,7 @@ static void net_rx_action(struct softirq
else
dev->quota = dev->weight;
} else {
- netpoll_poll_unlock(dev);
+ netpoll_poll_unlock(have);
dev_put(dev);
local_irq_disable();
}