linux-kernel - Re: [NETPOLL] netconsole: fix soft lockup when removing module

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Message-ID: <20070702092408.GA137@tv-sign.ru>
Date:	Mon, 2 Jul 2007 13:24:08 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [NETPOLL] netconsole: fix soft lockup when removing module

On 07/02, Jarek Poplawski wrote:
>
> > > --- a/net/core/netpoll.c
> > > +++ b/net/core/netpoll.c
> > > @@ -72,7 +72,8 @@ static void queue_process(struct work_struct *work)
> > >  			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;
> > >  		}
>
> [...snip...]
> 
> So, 2.6.21 needs something better (maybe you've found it btw.?),
> but they weren't too interested, anyway.

We can do a double flush trick. If queue_process() checks ->refcnt before
schedule_delayed_work() like above, netpoll_cleanup() can do

	flush_scheduled_work();

	// the next invocation of queue_process()
	// must see ->refcnt == 0
	if (!cancel_delayed_work(&npinfo->tx_work)) {
		/* may be queued, wait for completion */
		flush_scheduled_work();
	}

Jarek, I don't understand net/, a silly question. Why do we need the #2 chunk?
Isn't it better to move skb_queue_purge(&npinfo->txq) after cancel_..._work()
instead?

Oleg.	

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