[Xen-devel] Crash in netbk_gop_frag_copy?

Hi Dongxiao,

We're seeing a crash in netbk_gop_frag_copy and I was wondering if it
might related to the multithreaded/tasklet netback patches. This is in a
2.6.27 traditional Xen kernel but the most recent netback change made in
that tree was the backport of the multithread patches.

The crash appears to correspond to the "copy_gop->source.domid =
src_pend->netif->domid" line of netbk_gop_frag_copy, specifically
src_pend->netif seems to be NULL.

Have you seen anything like this?

One thing I did notice is that 020ba906 "xen/netback: Multiple tasklets
support." includes this hunk:
@@ -321,7 +331,8 @@ static u16 netbk_gop_frag(struct xen_netif *netif, struct 
netbk_rx_meta *meta,
 
        copy_gop = npo->copy + npo->copy_prod++;
        copy_gop->flags = GNTCOPY_dest_gref;
-       if (idx > -1) {
+       if (PageForeign(page)) {
+               struct xen_netbk *netbk = &xen_netbk[group];
                struct pending_tx_info *src_pend = &netbk->pending_tx_info[idx];
                copy_gop->source.domid = src_pend->netif->domid;
                copy_gop->source.u.ref = src_pend->req.gref;

I'm not sure it is guaranteed that all foreign pages which reach this
point are netback pages, is it? gnttab_copy_grant_page also sets
PageForeign for example.

Does this change relate to the removal of the 
       if ((idx >= MAX_PENDING_REQS) || (netbk->mmap_pages[idx] != pg))
               return -1;
check from netif_page_index in a3031942 "xen/netback: Introduce a new
struct type page_ext."?

Do you think we perhaps need to reinstate a similar check to this as
well as first checking that group is a sensible offset into the
xen_netbk array?

Thanks,
Ian.

[2010-07-11 03:50:28 UTC] BUG: unable to handle kernel paging request at
f0052dac
[2010-07-11 03:50:28 UTC] IP: [<c0284ed8>] netbk_gop_frag_copy+0x78/0x200
[2010-07-11 03:50:28 UTC] Oops: 0000 [#1] SMP 
[2010-07-11 03:50:28 UTC] last sysfs file: 
/sys/devices/xen-backend/vbd-1669-51712/statistics/rd_usecs
[2010-07-11 03:50:28 UTC] Modules linked in: tun nfs nfs_acl dm_round_robin 
scsi_dh_emc dm_multipath scsi_dh bonding hfsplus lockd sunrpc bridge stp llc(N) 
ipt_REJECT nf_conntrack_ipv4 xt_state nf_conntrack xt_tcpudp iptable_filter 
ip_tables x_tables binfmt_misc nls_utf8 isofs(N) sbs sbshc fan battery ac 
parport_pc lp parport nvram sg evdev(N) usb_storage libusual(N) container bnx2 
zlib_inflate(N) usbhid thermal ff_memless qla2xxx processor button thermal_sys 
hpilo scsi_transport_fc e1000e piix serio_raw 8250_pnp ide_cd_mod 8250 cdrom 
serial_core ata_piix libata dock rtc_cmos rtc_core rtc_lib pcspkr ide_generic 
dm_snapshot dm_zero dm_mirror dm_log dm_mod ide_disk cciss sd_mod scsi_mod ext3 
jbd uhci_hcd ohci_hcd ehci_hcd usbcore fbcon(N) font(N) tileblit(N) bitblit(N) 
softcursor(N)
[2010-07-11 03:50:28 UTC] Supported: No, Unsupported modules are loaded
[2010-07-11 03:50:28 UTC] 
[2010-07-11 03:50:28 UTC] Pid: 1173, comm: netback/2 Tainted: G          
(2.6.27.45-0.1.1.xs5.6.900.128.111247xen #1)
[2010-07-11 03:50:28 UTC] EIP: 0061:[<c0284ed8>] EFLAGS: 00010246 CPU: 0
[2010-07-11 03:50:28 UTC] EIP is at netbk_gop_frag_copy+0x78/0x200
[2010-07-11 03:50:28 UTC] EAX: f0052d9c EBX: f0087384 ECX: 00000000 EDX: 
f0052cfc
[2010-07-11 03:50:28 UTC] ESI: 00000006 EDI: eccfbf44 EBP: eccfbee0 ESP: 
eccfbec0
[2010-07-11 03:50:28 UTC]  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0069
[2010-07-11 03:50:28 UTC] Process netback/2 (pid: 1173, ti=eccfa000 
task=ed81d030 task.ti=eccfa000)
[2010-07-11 03:50:28 UTC] Stack: c15a8ba0 cdfb2480 ffff1cfc f008ad3c 00000000 
00000006 0000000c 00000001 
[2010-07-11 03:50:28 UTC]        eccfbfa4 c02852b4 00000006 000000d2 00000000 
c16bdb34 eccfbf88 eccfbf20 
[2010-07-11 03:50:28 UTC]        f008730c f008630c eca73bdc f008530c 00000001 
f007d630 eea80200 ed81d030 
[2010-07-11 03:50:28 UTC] Call Trace:
[2010-07-11 03:50:28 UTC]  [<c02852b4>] ? net_rx_action+0x254/0x920
[2010-07-11 03:50:28 UTC]  [<c0287407>] ? netbk_action_thread+0x97/0x170
[2010-07-11 03:50:28 UTC]  [<c013de00>] ? autoremove_wake_function+0x0/0x50
[2010-07-11 03:50:28 UTC]  [<c0287370>] ? netbk_action_thread+0x0/0x170
[2010-07-11 03:50:28 UTC]  [<c013daa2>] ? kthread+0x42/0x70
[2010-07-11 03:50:28 UTC]  [<c013da60>] ? kthread+0x0/0x70
[2010-07-11 03:50:28 UTC]  [<c010569b>] ? kernel_thread_helper+0x7/0x10
[2010-07-11 03:50:28 UTC]  =======================
[2010-07-11 03:50:28 UTC] Code: 69 db 04 e3 00 00 8d 04 40 8d 54 82 f4 89 55 ec 
89 5d e8 eb 65 8b 45 f0 8b 55 e8 03 15 a8 94 53 c0 c1 e0 04 8d 84 10 a0 00 00 
00 <8b> 50 10 0f b7 12 66 89 53 04 8b 40 04 66 c7 43 12 03 00 89 03 
[2010-07-11 03:50:28 UTC] EIP: [<c0284ed8>] netbk_gop_frag_copy+0x78/0x200 
SS:ESP 0069:eccfbec0
[2010-07-11 03:50:28 UTC] ---[ end trace cf7f02bf1fe43242 ]---


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[Xen-devel] Crash in netbk_gop_frag_copy?
