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From: Andrew Morton <akpm@linux-foundation.org>
To: Jarek Poplawski <jarkao2@gmail.com>
Cc: netdev@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	linux-kernel@vger.kernel.org,
	Stephen Hemminger <shemminger@linux-foundation.org>,
	"Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: locking api self-test hanging
Date: Tue, 4 Mar 2008 01:10:50 -0800	[thread overview]
Message-ID: <20080304011050.74f30dd3.akpm@linux-foundation.org> (raw)
In-Reply-To: <20080304084024.GA3980@ff.dom.local>

On Tue, 4 Mar 2008 08:40:24 +0000 Jarek Poplawski <jarkao2@gmail.com> wrote:

> On 04-03-2008 06:05, Andrew Morton wrote:
> ...
> >>>> And I've fully bisected this hang twice and both times came up with
> >>>>
> >>>> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> >>>> Author: Stephen Hemminger <shemminger@linux-foundation.org>
> >>>> Date:   Mon Nov 19 19:24:52 2007 -0800
> >>>>
> >>>>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> >>>>
> >>>> which is stupid because that patch doesn't do anything.
> 
> ...or maybe apparently doesn't do anything?
> 
> @@ -128,13 +127,11 @@ 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;
> 
> 
> But in a next patch we can see:
> 
> @@ -51,12 +50,12 @@ static inline int netpoll_rx(struct sk_buff *skb)
>         unsigned long flags;
>         int ret = 0;
>  
> -       if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
> +       if (!npinfo || !npinfo->rx_np)
> 
> So, it seems rx_flags could have been tested here for NETPOLL_RX_DROP
> yet?
> 

Oh damn.  I bisected this three times and the second two times both landed on
this:


commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
Author: Stephen Hemminger <shemminger@linux-foundation.org>
Date:   Mon Nov 19 19:24:52 2007 -0800

    [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
    
    Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index cf6acd3..9e3aea0 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -40,7 +40,6 @@ 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) + \
@@ -128,13 +127,11 @@ 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;
 }
@@ -475,7 +472,7 @@ int __netpoll_rx(struct sk_buff *skb)
 	if (skb->dev->type != ARPHRD_ETHER)
 		goto out;
 
-	/* check if netpoll clients need ARP */
+	/* if receive ARP during middle of NAPI poll, then queue */
 	if (skb->protocol == htons(ETH_P_ARP) &&
 	    atomic_read(&trapped)) {
 		skb_queue_tail(&npi->arp_tx, skb);
@@ -537,6 +534,9 @@ 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;

and I stupidly assumed that it couldn't be this commit because it was a
no-op.  I didn't think to look for an _impicit_ test of NETPOLL_RX_DROP
such as the one above.  That's pretty poor style IMO :(


That bisecting took me several hours and at the time I hoped that it would
receive a more-than-zero response.  btw.


  reply	other threads:[~2008-03-04  9:11 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-03 23:02 Andrew Morton
2008-02-03 23:07 ` Andrew Morton
2008-02-04 12:43   ` Andrew Morton
2008-02-04 13:04     ` Andrew Morton
2008-02-04 13:14       ` Peter Zijlstra
2008-02-05 13:23       ` Bernhard Walle
2008-02-04 13:18     ` Andrew Morton
2008-02-06  8:34     ` Andrew Morton
2008-02-06  9:16       ` Andrew Morton
2008-03-04  5:05         ` Andrew Morton
2008-03-04  8:06           ` [patch] mark netconsole broken Ingo Molnar
2008-03-04 16:19             ` Randy Dunlap
2008-03-04 20:30             ` David Miller
2008-03-04 20:52               ` Ingo Molnar
2008-03-04  8:40           ` locking api self-test hanging Jarek Poplawski
2008-03-04  9:10             ` Andrew Morton [this message]
2008-03-04 19:04           ` Marcin Slusarz

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