From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Durrant Subject: Re: Xen-unstable Linux 3.14-rc3 and 3.13 Network troubles "bisected" Date: Wed, 26 Mar 2014 17:46:06 +0000 Message-ID: <9AAE0902D5BC7E449B7C8E4E778ABCD029B350__23037.4189479791$1395856061$gmane$org@AMSPEX01CL01.citrite.net> References: <1744594108.20140318162127@eikelenboom.it> <20140318160412.GB16807@zion.uk.xensource.com> <1701035622.20140318211402@eikelenboom.it> <722971844.20140318221859@eikelenboom.it> <1688396550.20140319001104@eikelenboom.it> <20140319113532.GD16807@zion.uk.xensource.com> <246793256.20140319220752@eikelenboom.it> <20140321164958.GA31766@zion.uk.xensource.com> <1334202265.20140321182727@eikelenboom.it> <1056661597.20140322192834@eikelenboom.it> <20140325151539.GG31766@zion.uk.xensource.com> <79975567.20140325162942@eikelenboom.it> <1972209744.20140326121116@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029AD94@AMSPEX01CL01.citrite.net> <1715463578.20140326162245@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029AFC1@AMSPEX01CL01.citrite.net> <799579453.20140326170641@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029B106@AMSPEX01CL01.citrite.net> <789809468.20140326175352@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029B277@AMSPEX01CL01.citrite.net> <966386043.20140326183304@eikelenboom.it> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <966386043.20140326183304@eikelenboom.it> Content-Language: en-US List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Sander Eikelenboom Cc: Wei Liu , Ian Campbell , "netdev@vger.kernel.org" , linux-kernel , "xen-devel@lists.xen.org" , annie li , Zoltan Kiss List-Id: xen-devel@lists.xenproject.org Re-send shortened version... > -----Original Message----- > From: Sander Eikelenboom [mailto:linux@eikelenboom.it] > Sent: 26 March 2014 16:54 > To: Paul Durrant > Cc: Wei Liu; annie li; Zoltan Kiss; xen-devel@lists.xen.org; Ian Campbell; linux- > kernel; netdev@vger.kernel.org > Subject: Re: [Xen-devel] Xen-unstable Linux 3.14-rc3 and 3.13 Network > troubles "bisected" > [snip] > >> > >> - When processing an SKB we end up in "xenvif_gop_frag_copy" while > prod > >> == cons ... but we still have bytes and size left .. > >> - start_new_rx_buffer() has returned true .. > >> - so we end up in get_next_rx_buffer > >> - this does a RING_GET_REQUEST and ups cons .. > >> - and we end up with a bad grant reference. > >> > >> Sometimes we are saved by the bell .. since additional slots have become > >> free (you see cons become > prod in "get_next_rx_buffer" but shortly > after > >> that prod is increased .. > >> just in time to not cause a overrun). > >> > > > Ah, but hang on... There's a BUG_ON meta_slots_used > > max_slots_needed, so if we are overflowing the worst-case calculation then > why is that BUG_ON not firing? > > You mean: > sco = (struct skb_cb_overlay *)skb->cb; > sco->meta_slots_used = xenvif_gop_skb(skb, &npo); > BUG_ON(sco->meta_slots_used > max_slots_needed); > > in "get_next_rx_buffer" ? > That code excerpt is from net_rx_action(),isn't it? > I don't know .. at least now it doesn't crash dom0 and therefore not my > complete machine and since tcp is recovering from a failed packet :-) > Well, if the code calculating max_slots_needed were underestimating then the BUG_ON() should fire. If it is not firing in your case then this suggests your problem lies elsewhere, or that meta_slots_used is not equal to the number of ring slots consumed. > But probably because "npo->copy_prod++" seems to be used for the frags .. > and it isn't added to npo->meta_prod ? > meta_slots_used is calculated as the value of meta_prod at return (from xenvif_gop_skb()) minus the value on entry , and if you look back up the code then you can see that meta_prod is incremented every time RING_GET_REQUEST() is evaluated. So, we must be consuming a slot without evaluating RING_GET_REQUEST() and I think that's exactly what's happening... Right at the bottom of xenvif_gop_frag_copy() req_cons is simply incremented in the case of a GSO. So the BUG_ON() is indeed off by one. Paul