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 <[email protected]>
> >
> > Do not call cancel_rearming_delayed_work() if there is no
> > pending work.
> >
> > Signed-off-by: Jason Wessel <[email protected]>
> > Signed-off-by: Andrew Morton <[email protected]>
> > ---
> >
> > 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 <[email protected]>
---
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);
}
}
-
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