From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH] add netconsole support for xen-netfront Date: Wed, 18 Jan 2012 08:59:36 +0000 Message-ID: <1326877176.29475.37.camel@dagon.hellion.org.uk> References: <1326271956-25565-1-git-send-email-zhenzhong.duan@oracle.com> <20120112141745.GA7685@phenom.dumpdata.com> <1326452769.17210.331.camel@zakaz.uk.xensource.com> <4F15EB3E.3060700@oracle.com> <20120117215100.GA25367@phenom.dumpdata.com> <4F160113.1030503@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F160113.1030503@oracle.com> Sender: linux-kernel-owner@vger.kernel.org To: Tina Yang Cc: Konrad Rzeszutek Wilk , Zhenzhong Duan , "xen-devel@lists.xensource.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "gurudas.pai@oracle.com" , Jeremy Fitzhardinge List-Id: xen-devel@lists.xenproject.org On Tue, 2012-01-17 at 23:15 +0000, Tina Yang wrote: > On 1/17/2012 1:51 PM, Konrad Rzeszutek Wilk wrote: > > On Tue, Jan 17, 2012 at 01:42:22PM -0800, Tina Yang wrote: > >> On 1/13/2012 3:06 AM, Ian Campbell wrote: > >> Although netdump is now obsolete, I think it's always a good practice > >> to preserve caller's irq status as we had a very bad experience > >> chasing a similar problem caused by such a irq change in RDS > > Did you find the culprit of it? Was there a patch for that in the > > upstream kernel? > Yes. It has nothing to do with net drivers but same cause > elsewhere in the kernel. I didn't think start_xmit could be called with interrupts disabled or from interrupt context but perhaps I am wrong about that or perhaps netconsole changes things? Right, Documentation/networking/netdevices.txt states that start_xmit can be called with interrupts disabled by netconsole and therefore using the irqsave/restore locking in this function is, AFAICT, correct. > >> in the not too long ago past. > > OK, it sounds like it was issues in the past but might not be the > > case anymore. > > > > Could please re-test it without that spinlock irqsave patch using > > the upstream kernel (or just UEK2 since it is an 3.0 type kernel). > Shouldn't be the case now, but don't know about the future. > The fact is as long as there is a new caller that has the expectation > of preserved irq status, it would be a problem. The question is not so much what may or may not be a problem in the future but what the requirements of this function are, in particular those imposed by the network stack for the start_xmit function. > As Ian said, some net drivers have been cautious in this regard already by > saving/restoring the status, but apparently not everyone. I was talking about the interrupt/poll handler here since I hadn't yet noticed that the locking change was also in start_xmit and not just the poll/interrupt paths (which was actually just code motion and not a locking change in any case). Ian.