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 20:57:09 +0100 Message-ID: <172833073.20140326205709__42687.7853264616$1395863938$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> <9AAE0902D5BC7E449B7C8E4E778ABCD029B375@AMSPEX01CL01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD029B375@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, 6:48:15 PM, you wrote: >> -----Original Message----- >> From: Paul Durrant >> Sent: 26 March 2014 17:47 >> To: 'Sander Eikelenboom' >> 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" >> >> 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. >> > Can you re-test with the following patch applied? > Paul > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback > index 438d0c0..4f24220 100644 > --- a/drivers/net/xen-netback/netback.c > +++ b/drivers/net/xen-netback/netback.c > @@ -482,6 +482,8 @@ static void xenvif_rx_action(struct xenvif *vif) > while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) { > RING_IDX max_slots_needed; > + RING_IDX old_req_cons; > + RING_IDX ring_slots_used; > int i; > /* We need a cheap worse case estimate for the number of > @@ -511,8 +513,12 @@ static void xenvif_rx_action(struct xenvif *vif) > vif->rx_last_skb_slots = 0; > sco = (struct skb_cb_overlay *)skb->cb; > + > + old_req_cons = vif->rx.req_cons; > sco->meta_slots_used = xenvif_gop_skb(skb, &npo); > - BUG_ON(sco->meta_slots_used > max_slots_needed); > + ring_slots_used = vif->rx.req_cons - old_req_cons; > + > + BUG_ON(ring_slots_used > max_slots_needed); > __skb_queue_tail(&rxq, skb); > } That blew pretty fast .. on that BUG_ON [ 290.218182] ------------[ cut here ]------------ [ 290.225425] kernel BUG at drivers/net/xen-netback/netback.c:664! [ 290.232717] invalid opcode: 0000 [#1] SMP [ 290.239875] Modules linked in: [ 290.246923] CPU: 0 PID: 10447 Comm: vif7.0 Not tainted 3.13.6-20140326-nbdebug35+ #1 [ 290.254040] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640) , BIOS V1.8B1 09/13/2010 [ 290.261313] task: ffff880055d16480 ti: ffff88004cb7e000 task.ti: ffff88004cb7e000 [ 290.268713] RIP: e030:[] [] xenvif_rx_action+0x1650/0x1670 [ 290.276193] RSP: e02b:ffff88004cb7fc28 EFLAGS: 00010202 [ 290.283555] RAX: 0000000000000006 RBX: ffff88004c630000 RCX: 3fffffffffffffff [ 290.290908] RDX: 00000000ffffffff RSI: ffff88004c630940 RDI: 0000000000048e7b [ 290.298325] RBP: ffff88004cb7fde8 R08: 0000000000007bc9 R09: 0000000000000005 [ 290.305809] R10: ffff88004cb7fd28 R11: ffffc90012690600 R12: 0000000000000004 [ 290.313217] R13: ffff8800536a84e0 R14: 0000000000000001 R15: ffff88004c637618 [ 290.320521] FS: 00007f1d3030c700(0000) GS:ffff88005f600000(0000) knlGS:0000000000000000 [ 290.327839] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b [ 290.335216] CR2: ffffffffff600400 CR3: 0000000058537000 CR4: 0000000000000660 [ 290.342732] Stack: [ 290.350129] ffff88004cb7fd2c ffff880000000005 ffff88004cb7fd28 ffffffff810f7fc8 [ 290.357652] ffff880055d16b50 ffffffff00000407 ffff880000000000 ffffffff00000000 [ 290.365048] ffff880055d16b50 ffff880000000001 ffff880000000001 ffffffff00000000 [ 290.372461] Call Trace: [ 290.379806] [] ? __lock_acquire+0x418/0x2220 [ 290.387211] [] ? finish_task_switch+0x46/0xf0 [ 290.394552] [] xenvif_kthread+0x40/0x190 [ 290.401808] [] ? __init_waitqueue_head+0x60/0x60 [ 290.408993] [] ? xenvif_stop_queue+0x60/0x60 [ 290.416238] [] kthread+0xe4/0x100 [ 290.423428] [] ? _raw_spin_unlock_irq+0x30/0x50 [ 290.430615] [] ? __init_kthread_worker+0x70/0x70 [ 290.437793] [] ret_from_fork+0x7c/0xb0 [ 290.444945] [] ? __init_kthread_worker+0x70/0x70 [ 290.452091] Code: fd ff ff 48 8b b5 f0 fe ff ff 48 c7 c2 10 98 ce 81 31 c0 48 8b be c8 7c 00 00 48 c7 c6 f0 f1 fd 81 e8 35 be 24 00 e9 ba f8 ff ff <0f> 0b 0f 0b 41 bf 01 00 00 00 e9 55 f6 ff ff 0f 0b 66 66 66 66 [ 290.467121] RIP [] xenvif_rx_action+0x1650/0x1670 [ 290.474436] RSP [ 290.482400] ---[ end trace 2fcf9e9ae26950b3 ]---