Re: [Xen-devel] dom0 panic when using xm block-attach/block-detach -f

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am 13.01.2010 schrieb Pasi Kärkkäinen:
> On Wed, Jan 13, 2010 at 11:54:27AM +0100, Dietmar Hahn wrote:
> > Am 13.01.2010 schrieb Pasi Kärkkäinen:
> > > On Wed, Jan 13, 2010 at 11:13:50AM +0100, Dietmar Hahn wrote:
> > > > Am 13.01.2010 schrieb Pasi Kärkkäinen:
> > > > > On Wed, Jan 13, 2010 at 10:23:17AM +0100, Dietmar Hahn wrote:
> > > > > > Hi list,
> > > > > > 
> > > > > > I tried to verify my problem with xen-4.0.0-rc1.
> > > > > >
> > > > > 
> > > > > What dom0 kernel did you use? What kernel did you use in the guest?
> > > > 
> > > > The pv_ops kernel downloaded during make world:
> > > > # uname -a
> > > > Linux chiana 2.6.31.6-xen-400rc1 #6 SMP Wed Jan 13 10:43:49 CET 2010 
> > > > x86_64 x86_64 x86_64 GNU/Linux
> > > > 
> > > > I only added ext4 to the config because the Linux-partition is ext4 ;-)
> > > >
> > > 
> > > Ok. 
> > > 
> > > I'm not sure if block-attach to dom0 has ever been supported? 
> > > Did it work at some point for you? 
> > > 
> > > -- Pasi
> > 
> > As you can see in my first mail below this works in openSuse-11.2 with
> > xen-4.3 and linux-2.6.31.5.
> >
> 
> Ok.. It shouldn't crash, even if it doesn't work.
> Someone should investigate this more in depth..
> 
> Out of curiosity, why do you want to do that? :) kpartx is much more
> simple, and doesn't need Xen at all to do the same..

It was not my idea. A vm-install tool used these commands to extract the
kernel and the initrd from the image. I only analyzed the dom0 panics
and could reproduce the panic with these commands.
I will talk to the tool writer.

Dietmar.

> > 
> > > 
> > > > Dietmar.
> > > > 
> > > > > 
> > > > > -- Pasi
> > > > > 
> > > > > 
> > > > > > I did again the block-attach:
> > > > > > 
> > > > > > # xm block-attach 0 tap:aio:my-image.iso xvda r
> > > > > > 
> > > > > > But now I don't get any devices /dev/xvda?
> > > > > > Now I'am a little bit confused!
> > > > > > 
> > > > > > # fdisk -l my-image.iso
> > > > > > You must set cylinders.
> > > > > > You can do this from the extra functions menu.
> > > > > > 
> > > > > > Disk my-image.iso: 0 MB, 0 bytes
> > > > > > 255 heads, 63 sectors/track, 0 cylinders
> > > > > > Units = cylinders of 16065 * 512 = 8225280 bytes
> > > > > > Disk identifier: 0x00044fcc
> > > > > > 
> > > > > >        Device Boot      Start         End      Blocks   Id  System
> > > > > > my-image.iso1               1          17      136521   82  Linux 
> > > > > > swap / Solaris
> > > > > > my-image.iso2   *          18         522     4056412+  83  Linux
> > > > > > 
> > > > > > Any help would be appreciated.
> > > > > > Thanks.
> > > > > > 
> > > > > > Dietmar.
> > > > > > 
> > > > > > Am 08.01.2010 schrieb Dietmar Hahn:
> > > > > > > Hi list,
> > > > > > > 
> > > > > > > I have an image with a bootable system and do the following steps:
> > > > > > > # xm block-attach 0 tap:aio:my-image.iso xvda r
> > > > > > > mount the root partition:
> > > > > > > # mount /dev/xvda2 /mnt
> > > > > > > Now forcing block-detach:
> > > > > > > # xm block-detach 0 51712 -f
> > > > > > > 
> > > > > > > This leads to an inconsistent sysfs in dom0.
> > > > > > > The xen device /sys/devices/xen/vbd-51712 gets removed but lots 
> > > > > > > of links remain.
> > > > > > > 
> > > > > > > In the log I can see the message:
> > > > > > > [  349.928350] vbd vbd-51712: 16 Device in use; refusing to close
> > > > > > > 
> > > > > > > The next call of
> > > > > > > # xm block-attach 0 tap:aio:my-image.iso xvda r
> > > > > > > leads to the panic, because creating of a sysfs entry failed
> > > > > > > (it's already there) and a not existing failure handling (return 
> > > > > > > of
> > > > > > > register_disk() in add_disk()) leads to the panic later.
> > > > > > > 
> > > > > > > [  210.184660] WARNING: at 
> > > > > > > /usr/src/linux-2.6.31.5-0.1/fs/sysfs/dir.c:489 
> > > > > > > sysfs_add_one+0xde/0x150()
> > > > > > > [  210.184662] Hardware name: CELSIUS H270
> > > > > > > [  210.184663] sysfs: cannot create duplicate filename 
> > > > > > > '/dev/block/202:0'
> > > > > > > [  210.184664] Modules linked in: ext4 jbd2 crc16 netbk blkbk 
> > > > > > > blkback_pagemap snd_pcm_oss snd_mixer_oss blktap snd_seq 
> > > > > > > snd_seq_device edd ipv6 af_packet bridge stp llc fuse loop dm_mod 
> > > > > > > arc4 ecb cryptomgr aead pcompress snd_hda_codec_realtek 
> > > > > > > crypto_blkcipher crypto_hash crypto_algapi snd_hda_intel iwlagn 
> > > > > > > snd_hda_codec iwlcore pcmcia snd_hwdep led_class snd_pcm ppdev 
> > > > > > > mac80211 snd_timer 8250_pci yenta_socket parport_pc 8250_pnp snd 
> > > > > > > tpm_infineon rsrc_nonstatic i2c_i801 parport iTCO_wdt 8250 
> > > > > > > soundcore cfg80211 intel_agp tpm e1000e video pcmcia_core 
> > > > > > > i2c_core heci(C) iTCO_vendor_support sr_mod sg pcspkr serio_raw 
> > > > > > > joydev serial_core snd_page_alloc rfkill agpgart tpm_bios output 
> > > > > > > container battery button ac usbhid hid uhci_hcd ehci_hcd xenblk 
> > > > > > > cdrom xennet fan thermal processor thermal_sys hwmon 
> > > > > > > ide_pci_generic ide_core sata_sil24 ata_generic
> > > > > > > [  210.184697] Pid: 15, comm: xenwatch Tainted: G         C 
> > > > > > > 2.6.31.5-0.1-xen-hahn #9
> > > > > > > [  210.184698] Call Trace:
> > > > > > > [  210.184701]  [<ffffffff800117e9>] try_stack_unwind+0x189/0x1b0
> > > > > > > [  210.184704]  [<ffffffff8000f2c6>] dump_trace+0xa6/0x1e0
> > > > > > > [  210.184707]  [<ffffffff800112f4>] show_trace_log_lvl+0x64/0x90
> > > > > > > [  210.184710]  [<ffffffff80011343>] show_trace+0x23/0x40
> > > > > > > [  210.184712]  [<ffffffff80460e6e>] dump_stack+0x81/0x9e
> > > > > > > [  210.184717]  [<ffffffff8004cf50>] 
> > > > > > > warn_slowpath_common+0x80/0xd0
> > > > > > > [  210.184720]  [<ffffffff8004d02b>] warn_slowpath_fmt+0x4b/0x70
> > > > > > > [  210.184723]  [<ffffffff8018f48e>] sysfs_add_one+0xde/0x150
> > > > > > > [  210.184726]  [<ffffffff8018fb3b>] 
> > > > > > > sysfs_do_create_link+0x17b/0x200
> > > > > > > [  210.184729]  [<ffffffff8018fc21>] sysfs_create_link+0x21/0x40
> > > > > > > [  210.184732]  [<ffffffff802e0375>] device_add+0x1d5/0x620
> > > > > > > [  210.184734]  [<ffffffff80185e76>] register_disk+0x66/0x1c0
> > > > > > > [  210.184737]  [<ffffffff8022212b>] add_disk+0xcb/0x1b0
> > > > > > > [  210.184742]  [<ffffffffa0098cb4>] backend_changed+0x354/0x3a0 
> > > > > > > [xenblk]
> > > > > > > [  210.184746]  [<ffffffff802fb952>] otherend_changed+0xf2/0x1c0
> > > > > > > [  210.184749]  [<ffffffff802f931c>] 
> > > > > > > xenwatch_handle_callback+0x2c/0x80
> > > > > > > [  210.184752]  [<ffffffff802f9538>] xenwatch_thread+0x1c8/0x200
> > > > > > > [  210.184755]  [<ffffffff8006cf96>] kthread+0xb6/0xc0
> > > > > > > [  210.184758]  [<ffffffff8000d25a>] child_rip+0xa/0x20
> > > > > > > [  210.184760] ---[ end trace 2db54c629bf6d53c ]---
> > > > > > > ...
> > > > > > > 
> > > > > > > The problem seems to be that in backend_changed() the device is 
> > > > > > > seen as in use
> > > > > > > and so blkfront_closing() -> xlvbd_del() -> del_gendisk()
> > > > > > > isn't called to remove the links but later the xen device gets 
> > > > > > > removed.
> > > > > > > 
> > > > > > > What to do here?
> > > > > > > If a user of the -f flag "SHOULD know what he is doing" than the 
> > > > > > > manual page
> > > > > > > of the xm command has to be changed.
> > > > > > > Ohterwise how can this be solved?
> > > > > > > 
> > > > > > > Thanks.
> > > > > > > Dietmar.
> > > > > > > 
> > > > > > > This was testet on OpenSuSE-11.2 with xen-3.4 and linux-2.6.31.5,
> > > > > > > don't know about xen-unstable!
> > > > > > > 
> > > > > > > 
> > > > > 
> > > > > 
> > > 
> > > 

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