[PATCH 5/5] netpoll: fix up trapped logic

Matt Mackall
2004-08-26T20:29:01Z

From: Jeff Moyer <jmoyer@redhat.com>

This patch contains the updates necessary to fix the hangs in netconsole.
This includes the changing of trapped to an atomic_t, and the addition of a
netpoll_poll_lock. It also turns dev->netpoll_rx into a bitfield which is
used to keep from running the networking code from the netpoll_poll call
path.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Matt Mackall <mpm@selenic.com>

--- linux-2.6.7/net/core/netpoll.c.locking 2004-08-16 14:43:52.565309376 -0400
+++ linux-2.6.7/net/core/netpoll.c 2004-08-16 15:06:29.270058904 -0400
@@ -36,7 +36,11 @@ static struct sk_buff *skbs;
static spinlock_t rx_list_lock = SPIN_LOCK_UNLOCKED;
static LIST_HEAD(rx_list);

-static int trapped;
+static atomic_t trapped;
+spinlock_t netpoll_poll_lock = SPIN_LOCK_UNLOCKED;
+
+#define NETPOLL_RX_ENABLED 1
+#define NETPOLL_RX_DROP 2

#define MAX_SKB_SIZE \
(MAX_UDP_CHUNK + sizeof(struct udphdr) + \
@@ -68,6 +72,7 @@ void netpoll_poll(struct netpoll *np)
* timeouts. Thus, we set our budget to a more reasonable value.
*/
int budget = 16;
+ unsigned long flags;

if(!np->dev || !netif_running(np->dev) || !np->dev->poll_controller)
return;
@@ -76,9 +81,19 @@ void netpoll_poll(struct netpoll *np)
np->dev->poll_controller(np->dev);

/* If scheduling is stopped, tickle NAPI bits */
- if(trapped && np->dev->poll &&
- test_bit(__LINK_STATE_RX_SCHED, &np->dev->state))
+ spin_lock_irqsave(&netpoll_poll_lock, flags);
+ if (np->dev->poll &&
+ test_bit(__LINK_STATE_RX_SCHED, &np->dev->state)) {
+ np->dev->netpoll_rx |= NETPOLL_RX_DROP;
+ atomic_inc(&trapped);
+
np->dev->poll(np->dev, &budget);
+
+ atomic_dec(&trapped);
+ np->dev->netpoll_rx &= ~NETPOLL_RX_DROP;
+ }
+ spin_unlock_irqrestore(&netpoll_poll_lock, flags);
+
zap_completion_queue();
}

@@ -355,7 +370,8 @@ int netpoll_rx(struct sk_buff *skb)
goto out;

/* check if netpoll clients need ARP */
- if (skb->protocol == __constant_htons(ETH_P_ARP) && trapped) {
+ if (skb->protocol == __constant_htons(ETH_P_ARP) &&
+ atomic_read(&trapped)) {
arp_reply(skb);
return 1;
}
@@ -418,7 +434,7 @@ int netpoll_rx(struct sk_buff *skb)
spin_unlock_irqrestore(&rx_list_lock, flags);

out:
- return trapped;
+ return atomic_read(&trapped);
}

int netpoll_parse_options(struct netpoll *np, char *opt)
@@ -609,7 +625,7 @@ int netpoll_setup(struct netpoll *np)
if(np->rx_hook) {
unsigned long flags;

- np->dev->netpoll_rx = 1;
+ np->dev->netpoll_rx = NETPOLL_RX_ENABLED;

spin_lock_irqsave(&rx_list_lock, flags);
list_add(&np->rx_list, &rx_list);
@@ -639,12 +655,15 @@ void netpoll_cleanup(struct netpoll *np)

int netpoll_trap(void)
{
- return trapped;
+ return atomic_read(&trapped);
}

void netpoll_set_trap(int trap)
{
- trapped = trap;
+ if (trap)
+ atomic_inc(&trapped);
+ else
+ atomic_dec(&trapped);
}

EXPORT_SYMBOL(netpoll_set_trap);

--
Mathematics is the supreme nostalgia of our time.