linux-kernel - Re: [hyperv] BUG at drivers/hv/channel.c:462 while changing MTU

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Message-ID: <20140825175029.GA25551@kroah.com>
Date:	Mon, 25 Aug 2014 10:50:29 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Sitsofe Wheeler <sitsofe@...il.com>,
	Jason Wang <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [hyperv] BUG at drivers/hv/channel.c:462 while changing MTU

On Mon, Aug 25, 2014 at 05:34:27PM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> > Sent: Monday, August 25, 2014 2:37 AM
> > To: Sitsofe Wheeler
> > Cc: KY Srinivasan; Greg Kroah-Hartman; Jason Wang; linux-
> > kernel@...r.kernel.org; David S. Miller; Daniel Borkmann;
> > netdev@...r.kernel.org; devel@...uxdriverproject.org; Haiyang Zhang
> > Subject: Re: [hyperv] BUG at drivers/hv/channel.c:462 while changing MTU
> > 
> > The code here is:
> > 
> > drivers/hv/channel.c
> >    460          BUG_ON(ret != 0);
> >    461          t = wait_for_completion_timeout(&info->waitevent, 5*HZ);
> >    462          BUG_ON(t == 0);
> > 
> > So it calls BUG_ON() if the teardown takes more than 5 seconds.  It's most
> > likely that there is a race condition somewhere.  It's also possible that it's just
> > taking longer than 5 seconds for some odd reason and the bug would go
> > away if we raised it to 60 seconds.
> > 
> > BUG_ON() after 5 seconds seems like a very aggressive thing.
> 
> Dan,
> 
> I am going to audit all BUG_ON() instances.

Please remove them all, no kernel driver should ever crash the kernel
and not give a user a chance to recover :(

thanks,

greg k-h
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