From: Jarek Poplawski <jarkao2@o2.pl>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Folkert van Heusden <folkert@vanheusden.com>,
linux-kernel@vger.kernel.org,
Jason Wessel <jason.wessel@windriver.com>,
Thomas Gleixner <tglx@linutronix.de>,
stable@kernel.org, netdev@vger.kernel.org
Subject: [PATCH] Re: [2.6.21.1] soft lockup when removing netconsole module
Date: Wed, 13 Jun 2007 11:25:37 +0200 [thread overview]
Message-ID: <20070613092537.GA2432@ff.dom.local> (raw)
In-Reply-To: <20070612110233.GA3281@ff.dom.local>
On Tue, Jun 12, 2007 at 01:02:33PM +0200, Jarek Poplawski wrote:
...
> Of course such a problem should preferably be fixed by somebody who
> knows the code (alas I don't know netconsole), to be sure all needed
> cancels are still done after this change. I hope Jason's patch is
> right but I'm a little surprised I can't see netdev in cc (I'll try
> to fix this).
So, I've had a look into netpoll and, unfortunately, I don't
think this patch is right...
> > From: Jason Wessel <jason.wessel@windriver.com>
> >
> > Do not call cancel_rearming_delayed_work() if there is no
> > pending work.
> >
> > Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >
> > net/core/netpoll.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff -puN net/core/netpoll.c~a net/core/netpoll.c
> > --- a/net/core/netpoll.c~a
> > +++ a/net/core/netpoll.c
> > @@ -784,8 +784,10 @@ void netpoll_cleanup(struct netpoll *np)
> > if (atomic_dec_and_test(&npinfo->refcnt)) {
> > skb_queue_purge(&npinfo->arp_tx);
> > skb_queue_purge(&npinfo->txq);
> > - cancel_rearming_delayed_work(&npinfo->tx_work);
> > - flush_scheduled_work();
> > + if (delayed_work_pending(&npinfo->tx_work)) {
> > + cancel_rearming_delayed_work(&npinfo->tx_work);
> > + flush_scheduled_work();
> > + }
> >
> > kfree(npinfo);
> > }
> > _
There are such possibilities:
1. After positive delayed_work_pending(&npinfo->tx_work) test
some work is queued, but there is no guarantee that when running
it'll rearm again, so cancel_rearming_delayed_work can loop again;
2. After negative delayed_work_pending(&npinfo->tx_work) test
a work is just running, eg. waiting on netif_tx_lock, while
kfree(npinfo) is done here (oops?!).
I've found an additional problem here with or without this patch:
after deleting a timer in cancel_rearming_delayed_work() there could
stay a last skb queued in npinfo->txq, and after kfree(npinfo)
we have small memory leak. If I'm right here similar fix is needed
in the current netpoll code: additional npinfo->txq purging only
or maybe the whole cancel_rearming_ changed like this.
I've tried to eliminate these problems in attached below patch
proposal. I'm not sure it's all right: as I've written earlier I
don't know netconsole enough, but it's probably a little better
than above solution.
I've some doubts yet (I didn't have time to check this all):
1. I hope this other schedule_delayed_work() from netpoll_send_skb()
is not possible when netpoll_cleanup() runs - if I'm wrong additional
check of npinfo->refcnt should be done there;
2. I also hope npinfo->refcnt before scheduling should be enough here
- if not - another possibility is adding some locking eg.:
netif_tx_lock before cancel for synchronization.
Of course it would be very nice if somebody could test or verify
this patch more.
Regards,
Jarek P.
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
---
diff -Nurp 2.6.21-/net/core/netpoll.c 2.6.21/net/core/netpoll.c
--- 2.6.21-/net/core/netpoll.c 2007-04-26 15:08:32.000000000 +0200
+++ 2.6.21/net/core/netpoll.c 2007-06-12 21:05:23.000000000 +0200
@@ -73,7 +73,8 @@ static void queue_process(struct work_st
netif_tx_unlock(dev);
local_irq_restore(flags);
- schedule_delayed_work(&npinfo->tx_work, HZ/10);
+ if (atomic_read(&npinfo->refcnt))
+ schedule_delayed_work(&npinfo->tx_work, HZ/10);
return;
}
netif_tx_unlock(dev);
@@ -780,9 +781,15 @@ void netpoll_cleanup(struct netpoll *np)
if (atomic_dec_and_test(&npinfo->refcnt)) {
skb_queue_purge(&npinfo->arp_tx);
skb_queue_purge(&npinfo->txq);
- cancel_rearming_delayed_work(&npinfo->tx_work);
+ cancel_delayed_work(&npinfo->tx_work);
flush_scheduled_work();
+ /* clean after last, unfinished work */
+ if (!skb_queue_empty(&npinfo->txq)) {
+ struct sk_buff *skb;
+ skb = __skb_dequeue(&npinfo->txq);
+ kfree_skb(skb);
+ }
kfree(npinfo);
}
}
next prev parent reply other threads:[~2007-06-13 9:18 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-26 15:40 [2.6.21.1] soft lockup when removing netconsole module Folkert van Heusden
2007-05-26 15:53 ` Parag Warudkar
2007-05-26 16:12 ` Thomas Gleixner
2007-05-26 16:17 ` Folkert van Heusden
2007-05-26 16:35 ` Thomas Gleixner
2007-05-26 16:49 ` Folkert van Heusden
2007-05-26 17:06 ` Thomas Gleixner
2007-05-26 17:12 ` Folkert van Heusden
2007-05-27 20:32 ` Matt Mackall
2007-05-29 7:56 ` Andrew Morton
2007-05-30 13:28 ` [PATCH] " Jason Wessel
2007-05-30 20:38 ` Folkert van Heusden
2007-06-12 11:02 ` Jarek Poplawski
2007-06-13 9:25 ` Jarek Poplawski [this message]
2007-06-26 23:07 ` [PATCH] " Andrew Morton
2007-06-27 0:46 ` Wessel, Jason
2007-06-27 1:00 ` Andrew Morton
2007-06-27 7:24 ` Jarek Poplawski
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