[Xen-devel] [BUG] kernel bug encountered at drivers/net/xen-netback/netback.c:430!

["Alex Braunegg" <alex.braunegg@xxxxxxxxx>]

Hi all,

I experienced the following bug whilst using a Xen VM. What happened was
that this morning a single Xen VM suddenly terminated without cause with the
following being logged in dmesg. 

Only 1 VM experienced an issue (out of 2 which were running), the other
remained up and fully functional until I attempted to restart the crashed VM
which triggered the kernel bug.

Kernel: 4.14.6
Xen:            4.8.2

============================================================================
=========

vif vif-2-0 vif2.0: Trying to unmap invalid handle! pending_idx: 0x3f
------------[ cut here ]------------
kernel BUG at drivers/net/xen-netback/netback.c:430!
invalid opcode: 0000 [#1] SMP
Modules linked in: xt_physdev(E) iptable_filter(E) ip_tables(E)
xen_netback(E) nfsd(E) lockd(E) grace(E) nfs_acl(E) auth_rpcgss(E) sunrpc(E)
ipmi_si(E) ipmi_msghandler(E) zfs(POE) zcommon(POE) znvpair(POE) icp(POE)
spl(OE) zavl(POE) zunicode(POE) k10temp(E) tpm_infineon(E) sp5100_tco(E)
i2c_piix4(E) i2c_core(E) ohci_pci(E) ohci_hcd(E) tg3(E) ptp(E) pps_core(E)
sg(E) raid1(E) sd_mod(E) ata_generic(E) pata_acpi(E) pata_atiixp(E) ahci(E)
libahci(E) dm_mirror(E) dm_region_hash(E) dm_log(E) dm_mod(E) dax(E)
CPU: 0 PID: 13163 Comm: vif2.0-q0-deall Tainted: P           OE
4.14.6-1.el6.x86_64 #1
Hardware name: HP ProLiant MicroServer, BIOS O41     10/01/2013
task: ffff8800595cc980 task.stack: ffffc900028e0000
RIP: e030:xenvif_tx_dealloc_action+0x1bb/0x230 [xen_netback]
RSP: e02b:ffffc900028e3c68 EFLAGS: 00010292
RAX: 0000000000000045 RBX: ffffc90002969000 RCX: 0000000000000000
RDX: ffff88007f4146e8 RSI: ffff88007f40db38 RDI: ffff88007f40db38
RBP: ffffc900028e3e98 R08: 000000000000037b R09: 000000000000037c
R10: 0000000000000001 R11: 0000000000000000 R12: ffffc90002972730
R13: 0000160000000000 R14: aaaaaaaaaaaaaaab R15: ffffc9000099bbe8
FS:  00007fee260ff9a0(0000) GS:ffff88007f400000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 0000000062815000 CR4: 0000000000000660
Call Trace:
 ? error_exit+0x5/0x20
 ? __update_load_avg_cfs_rq+0x176/0x180
 ? xen_mc_flush+0x87/0x120
 ? xen_load_sp0+0x84/0xa0
 ? __switch_to+0x1c1/0x360
 ? finish_task_switch+0x78/0x240
 ? __schedule+0x192/0x496
 ? _raw_spin_lock_irqsave+0x1a/0x3c
 ? _raw_spin_lock_irqsave+0x1a/0x3c
 ? _raw_spin_unlock_irqrestore+0x11/0x20
 xenvif_dealloc_kthread+0x68/0xf0 [xen_netback]
 ? do_wait_intr+0x80/0x80
 ? xenvif_map_frontend_data_rings+0xe0/0xe0 [xen_netback]
 kthread+0x106/0x140
 ? kthread_destroy_worker+0x60/0x60
 ? kthread_destroy_worker+0x60/0x60
 ret_from_fork+0x25/0x30
Code: 89 df 49 83 c4 02 e8 e5 f5 ff ff 4d 39 ec 75 e8 eb a2 48 8b 43 20 48
c7 c6 10 3b 55 a0 48 8b b8 20 03 00 00 31 c0 e8 85 b9 06 e1 <0f> 0b 0f 0b 48
8b 53 20 89 c1 48 c7 c6 48 3b 55 a0 31 c0 45 31 
RIP: xenvif_tx_dealloc_action+0x1bb/0x230 [xen_netback] RSP:
ffffc900028e3c68
---[ end trace 7d827dae67002ffc ]---

============================================================================
=========

The section of relevant kernel code is:

============================================================================
=========

static inline void xenvif_grant_handle_reset(struct xenvif_queue *queue,
                                             u16 pending_idx)
{
        if (unlikely(queue->grant_tx_handle[pending_idx] ==
                     NETBACK_INVALID_HANDLE)) {
                netdev_err(queue->vif->dev,
                           "Trying to unmap invalid handle! pending_idx:
0x%x\n",
                           pending_idx);
                BUG();
        }
        queue->grant_tx_handle[pending_idx] = NETBACK_INVALID_HANDLE;
}

============================================================================
=========

In an attempt to recover from this situation I restarted / destroyed (xl
restart <vmname> / xl destroy <vmname>) the VM to recover it's state and the
following error messages were logged at the console:

============================================================================
=========

libxl: error: libxl_exec.c:129:libxl_report_child_exitstatus:
/etc/xen/scripts/block remove [25271] died due to fatal signal Segmentation
fault
libxl: error: libxl_device.c:1080:device_backend_callback: unable to remove
device with path /local/domain/0/backend/vif/2/0
libxl: error: libxl.c:1647:devices_destroy_cb: libxl__devices_destroy failed
for 2

============================================================================
=========

After which the physical system hung, then the physical system restarted
with nothing else logged and everything came back OK & operational including
the VM that crashed.

Further details (xl dmesg, xl info) attached.

Best regards,

Alex Braunegg

Attachment: xl-dmesg.txt
Description: Text document

Attachment: xl-info.txt
Description: Text document

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