[Xen-devel] [BUG] xl devd segmentation fault on xl block-detach

[Reinis Martinsons <admin@xxxxxx>]

Hi,

I would like to report a problem with storage driver domain. When 
detaching 2 virtual block devices from the same domain provided by the 
same driver domain, this generates a segmentation fault in the driver 
domain `xl devd` process. I observed the same problem both when manually 
detaching block devices from Dom0 and when shutting down guest domains 
with several block devices.
For ease of demonstration I am sharing my test results on a simple 
scenario where virtual block devices are provided from a storage driver 
domain (DomD) back to Dom0, but I observed identical results for other 
DomUs.
Both of my Dom0 and DomD are Arch Linux (kernel 4.10.11-1-ARCH). I built 
xen from Arch Linux User Repository (https://aur.archlinux.org/xen.git) 
latest commit 16894c15a19bfef23550ba09d58e097fe16c4792, which is using 
Xen 4.8.0 (commit b03cee73197f4a37bf2941b9367105187355e638). Please see 
the output of `xl info` attached in "xl info (Dom0).txt". When building 
xen for DomD, I enabled debugging symbols (`debug ?= y` in /Config.mk). 
I enabled xendriverdomain.service in DomD. DomD configuration file is 
attached in "DomD.cfg".
After 2 consecutive `xl block-attach` and `xl block-detach` commands in 
Dom0 I am observing the following output:
[root@arch-test-dom0 ~]# xl block-attach 0 
'format=raw,backendtype=phy,backend=arch-zfs-test,vdev=xvda,target=/dev/zvol/test_pool/test1'
[root@arch-test-dom0 ~]# xl block-attach 0 
'format=raw,backendtype=phy,backend=arch-zfs-test,vdev=xvdb,target=/dev/zvol/test_pool/test2'
[root@arch-test-dom0 ~]# xl block-detach 0 51712
[root@arch-test-dom0 ~]# xl block-detach 0 51728
libxl: error: libxl_device.c:1264:device_destroy_be_watch_cb: timed out 
while waiting for /local/domain/1/backend/vbd/0/51728 to be removed
libxl: error: libxl.c:2009:device_addrm_aocomplete: unable to remove vbd 
with id 51728
libxl_device_disk_remove failed.

The 2nd `xl block-detach` command is generating segmentation fault in 
DomD `xl devd` process (search_for_guest (libxenlight.so.4.8)) - please 
see full DomD log output attached in "journalctl (domD).txt".
I am also attaching "xenstored-access.log" and output of `xenstore-ls 
-fp` in "xenstore-ls.txt". In addition, I am attaching output of gdb 
`backtrace full` command on the generated coredump in DomD as 
"coredumpctl gdb (DomD).txt"
Please let me know if I should provide any other information for 
debugging this problem.
Kind regards

Reinis Martinsons

Attachment: xl info (Dom0).txt
Description: Text document

Attachment: DomD.cfg
Description: Text document

Attachment: journalctl (domD).txt
Description: Text document

Attachment: xenstored-access.log
Description: Text document

Attachment: xenstore-ls.txt
Description: Text document

Attachment: coredumpctl gdb.txt
Description: Text document

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