From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sander Eikelenboom Subject: Re: Xen-unstable Linux 3.14-rc3 and 3.13 Network troubles "bisected" Date: Wed, 26 Mar 2014 19:07:52 +0100 Message-ID: <1959698732.20140326190752__14853.2801228159$1395857391$gmane$org@eikelenboom.it> 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> <9AAE0902D5BC7E449B7C8E4E778ABCD029B350@AMSPEX01CL01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD029B350@AMSPEX01CL01.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Paul Durrant 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 Wednesday, March 26, 2014, 6:46:06 PM, you wrote: > 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? Yes >> 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. It's seem to be the last .. [ 1157.188908] vif vif-7-0 vif7.0: ?!? xenvif_gop_skb Me here 5 npo->meta_prod:40 old_meta_prod:36 vif->rx.sring->req_prod:2105867 vif->rx.req_cons:2105868 meta->gso_type:1 meta->gso_size:1448 nr_frags:1 req->gref:657 req->id:7 estimated_slots_needed:4 j(data):1 reserved_slots_left:-1 used in funcstart: 0 + 1 .. used_dataloop:1 .. used_fragloop:3 [ 1157.244975] vif vif-7-0 vif7.0: ?!? xenvif_rx_action me here 2 .. vif->rx.sring->req_prod:2105867 vif->rx.req_cons:2105868 sco->meta_slots_used:4 max_upped_gso:1 skb_is_gso(skb):1 max_slots_needed:4 j:6 is_gso:1 nr_frags:1 firstpart:1 secondpart:2 reserved_slots_left:-1 net_rx_action() calculated we would need 4 slots .. and sco->meta_slots_used == 4 when we return so it doesn't trigger you BUG_ON .. The 4 slots we calculated are: 1 slot for the data part: DIV_ROUND_UP(offset_in_page(skb->data) + skb_headlen(skb), PAGE_SIZE) 2 slots for the single frag in this SKB from: DIV_ROUND_UP(size, PAGE_SIZE) 1 slot since GSO In the debug code i annotated all cons++, and the code uses 1 slot to process the data from the SKB as expected but uses 3 slots in the frag chopping loop. And when it reaches the state were cons > prod it is always in "get_next_rx_buffer". >> 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. That is probably only done on first iteration / frag ? Because i don't see my warn there trigger .. but it could be that's because at that moment we still have cons <= prod. > Paul