[NET]: Fix race between poll_napi() and net_rx_action()

netpoll_poll_lock() synchronizes the ->poll() invocation
code paths, but once we have the lock we have to make
sure that NAPI_STATE_SCHED is still set.  Otherwise we
get:

	cpu 0			cpu 1

	net_rx_action()		poll_napi()
	netpoll_poll_lock()	... spin on ->poll_lock
	->poll()
	  netif_rx_complete
	netpoll_poll_unlock()	acquire ->poll_lock()
				->poll()
				 netif_rx_complete()
				 CRASH

Based upon a bug report from Tina Yang.

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 853c8b5..02e7d83 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2172,7 +2172,15 @@ static void net_rx_action(struct softirq_action *h)
 
                weight = n->weight;
 
-               work = n->poll(n, weight);
+               /* This NAPI_STATE_SCHED test is for avoiding a race
+                * with netpoll's poll_napi().  Only the entity which
+                * obtains the lock and sees NAPI_STATE_SCHED set will
+                * actually make the ->poll() call.  Therefore we avoid
+                * accidently calling ->poll() when NAPI is not scheduled.
+                */
+               work = 0;
+               if (test_bit(NAPI_STATE_SCHED, &n->state))
+                       work = n->poll(n, weight);
 
                WARN_ON_ONCE(work > weight);
 

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index bf8d18f..c499b5c 100644 (file)
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -116,6 +116,29 @@ static __sum16 checksum_udp(struct sk_buff *skb, struct udphdr *uh,
  * network adapter, forcing superfluous retries and possibly timeouts.
  * Thus, we set our budget to greater than 1.
  */
+static int poll_one_napi(struct netpoll_info *npinfo,
+                        struct napi_struct *napi, int budget)
+{
+       int work;
+
+       /* net_rx_action's ->poll() invocations and our's are
+        * synchronized by this test which is only made while
+        * holding the napi->poll_lock.
+        */
+       if (!test_bit(NAPI_STATE_SCHED, &napi->state))
+               return budget;
+
+       npinfo->rx_flags |= NETPOLL_RX_DROP;
+       atomic_inc(&trapped);
+
+       work = napi->poll(napi, budget);
+
+       atomic_dec(&trapped);
+       npinfo->rx_flags &= ~NETPOLL_RX_DROP;
+
+       return budget - work;
+}
+
 static void poll_napi(struct netpoll *np)
 {
        struct netpoll_info *npinfo = np->dev->npinfo;
@@ -123,17 +146,13 @@ static void poll_napi(struct netpoll *np)
        int budget = 16;
 
        list_for_each_entry(napi, &np->dev->napi_list, dev_list) {
-               if (test_bit(NAPI_STATE_SCHED, &napi->state) &&
-                   napi->poll_owner != smp_processor_id() &&
+               if (napi->poll_owner != smp_processor_id() &&
                    spin_trylock(&napi->poll_lock)) {
-                       npinfo->rx_flags |= NETPOLL_RX_DROP;
-                       atomic_inc(&trapped);
-
-                       napi->poll(napi, budget);
-
-                       atomic_dec(&trapped);
-                       npinfo->rx_flags &= ~NETPOLL_RX_DROP;
+                       budget = poll_one_napi(npinfo, napi, budget);
                        spin_unlock(&napi->poll_lock);
+
+                       if (!budget)
+                               break;
                }
        }
 }