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SubjectRe: [patch] mark netconsole broken
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From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 4 Mar 2008 09:06:44 +0100

> i'd suggest the patch below, to mark it broken.

Why bother when we know what the bug is and can fix it? :-)

commit d9452e9f81e997cbd0c9bface8d2c2a4b064cc3e
Author: David S. Miller <davem@davemloft.net>
Date: Tue Mar 4 12:28:49 2008 -0800

[NETPOLL]: Revert two bogus cleanups that broke netconsole.

Based upon a report by Andrew Morton and code analysis done
by Jarek Poplawski.

This reverts 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7 ("[NETPOLL]:
Kill NETPOLL_RX_DROP, set but never tested.") and
c7b6ea24b43afb5749cb704e143df19d70e23dea ("[NETPOLL]: Don't need
rx_flags.").

The rx_flags did get tested for zero vs. non-zero and therefore we do
need those tests and that code which sets NETPOLL_RX_DROP et al.

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

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index a0525a1..e3d7959 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -25,6 +25,7 @@ struct netpoll {

struct netpoll_info {
atomic_t refcnt;
+ int rx_flags;
spinlock_t rx_lock;
struct netpoll *rx_np; /* netpoll that registered an rx_hook */
struct sk_buff_head arp_tx; /* list of arp requests to reply to */
@@ -50,12 +51,12 @@ static inline int netpoll_rx(struct sk_buff *skb)
unsigned long flags;
int ret = 0;

- if (!npinfo || !npinfo->rx_np)
+ if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
return 0;

spin_lock_irqsave(&npinfo->rx_lock, flags);
- /* check rx_np again with the lock held */
- if (npinfo->rx_np && __netpoll_rx(skb))
+ /* check rx_flags again with the lock held */
+ if (npinfo->rx_flags && __netpoll_rx(skb))
ret = 1;
spin_unlock_irqrestore(&npinfo->rx_lock, flags);

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 6faa128..4b7e756 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -39,6 +39,8 @@ static struct sk_buff_head skb_pool;
static atomic_t trapped;

#define USEC_PER_POLL 50
+#define NETPOLL_RX_ENABLED 1
+#define NETPOLL_RX_DROP 2

#define MAX_SKB_SIZE \
(MAX_UDP_CHUNK + sizeof(struct udphdr) + \
@@ -126,11 +128,13 @@ static int poll_one_napi(struct netpoll_info *npinfo,
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;
}
@@ -472,7 +476,7 @@ int __netpoll_rx(struct sk_buff *skb)
if (skb->dev->type != ARPHRD_ETHER)
goto out;

- /* if receive ARP during middle of NAPI poll, then queue */
+ /* check if netpoll clients need ARP */
if (skb->protocol == htons(ETH_P_ARP) &&
atomic_read(&trapped)) {
skb_queue_tail(&npi->arp_tx, skb);
@@ -534,9 +538,6 @@ int __netpoll_rx(struct sk_buff *skb)
return 1;

out:
- /* If packet received while already in poll then just
- * silently drop.
- */
if (atomic_read(&trapped)) {
kfree_skb(skb);
return 1;
@@ -675,6 +676,7 @@ int netpoll_setup(struct netpoll *np)
goto release;
}

+ npinfo->rx_flags = 0;
npinfo->rx_np = NULL;

spin_lock_init(&npinfo->rx_lock);
@@ -756,6 +758,7 @@ int netpoll_setup(struct netpoll *np)

if (np->rx_hook) {
spin_lock_irqsave(&npinfo->rx_lock, flags);
+ npinfo->rx_flags |= NETPOLL_RX_ENABLED;
npinfo->rx_np = np;
spin_unlock_irqrestore(&npinfo->rx_lock, flags);
}
@@ -797,6 +800,7 @@ void netpoll_cleanup(struct netpoll *np)
if (npinfo->rx_np == np) {
spin_lock_irqsave(&npinfo->rx_lock, flags);
npinfo->rx_np = NULL;
+ npinfo->rx_flags &= ~NETPOLL_RX_ENABLED;
spin_unlock_irqrestore(&npinfo->rx_lock, flags);
}


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