From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [Xen-users] kernel 3.9.2 - xen 4.2.2/4.3rc1 => BUG unable to handle kernel paging request netif_poll+0x49c/0xe8 Date: Tue, 21 May 2013 16:28:47 +0100 Message-ID: <20130521152846.GP32007@zion.uk.xensource.com> References: <8511913.uMAmUdIO30@eistomin.edss.local> <5196407602000078000D7040@nat28.tlf.novell.com> <1467946.TvW6SdLxLt@eistomin.edss.local> <1763543.Xm2ls0EQVV@eistomin.edss.local> <519B609402000078000D7998@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <519B609402000078000D7998@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Eugene Istomin , Wei Liu , Ian Campbell , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Tue, May 21, 2013 at 10:55:00AM +0100, Jan Beulich wrote: > >>> On 17.05.13 at 15:00, Eugene Istomin wrote: > > Bump, here it is: > > Okay, but I think we're still lacking information on what your > Dom0 kernel is. > > Ian, Wei - looking at the forward ported as well as the upstream > frontends, I'm wondering if there isn't a fundamental flaw in > ..._get_responses(): It allows up to MAX_SKB_FRAGS + 1 slots/ > frags, and ..._fill_frags() then fills as many fragments as got > queued onto the respective list. Only after both of them are done, > __pskb_pull_tail() gets invoked reducing the fragment count by > one if the condition is met that made ..._get_responses() bump > the limit by one. > > Am I overlooking something? I'm asking because working through > disassembly and register values of the dump Eugene had sent I > clearly see that ..._fill_frags() is processing the 18th fragment, > while in that kernel version MAX_SKB_FRAGS is only 17 (but > possibly, hence the first question above, the Dom0 kernel still is > one with MAX_SKB_FRAGS being 18, or the packet turns out to I have the same suspection. However I just did a quick hack to bump MAX_SKB_FRAGS to 20 in backend, DomU worked just fine. > be such that it fills 17 fragments and the header is smaller than > RX_COPY_THRESHOLD). It would be better to know more info about Dom0. Will need some time to figure out what's going on there. Wei. > Jan