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

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Message-ID: <47d946d0039f497f80a891bfa79c3920@BY2PR0301MB0711.namprd03.prod.outlook.com>
Date:	Mon, 25 Aug 2014 18:05:01 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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



> -----Original Message-----
> From: Greg Kroah-Hartman [mailto:gregkh@...uxfoundation.org]
> Sent: Monday, August 25, 2014 10:50 AM
> To: KY Srinivasan
> Cc: Dan Carpenter; Sitsofe Wheeler; 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
> 
> 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 :(

I will clean this up.

K. Y
> 
> thanks,
> 
> greg k-h
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