On Mon, Oct 21, 2019 at 02:32:15PM +0100, Ian Jackson wrote: > This call to guest_umount_lv is here for the benefit of ad-hoc reruns > of (eg) ts-guest-start tidy up any ad-hoc messing about (eg from > earlier runs of ts-debian-fixup or something). It is not needed in > production runs. > > Serendipitously, this osstest code discovered a bug in the Linux > blkback: when tearing down, it sets the backend state to 6 before it > has closed the underlying block devices. This ultimately means that > after "xl destroy" or "xl shutdown -w" there is a period when the > guest's open handle onto its storage is still open. This is wrong. > > This detection depends on us winning a tricky race. So it shows up in > osstest as a very low probability heisenbug. The bug is currently in > all versions of Linux and causing a bit of a nuisance. > > It would be best to add a proper check for this bug. However, this is > quite fiddly: really, it ought to be done as close to the xl command > completion as possible, in the same ssh invocation. That would > involve a fair bit of plumbing and ad-hocery. I don't think that > would be proportionate for such a low-impact bug. > > So instead in this patch I just disable this cleanup code in the > troublesome case, unless it is explicitly requested by the user > setting OSSTEST_GUEST_DISK_MOUNT_CLEANUP to a trueish value. (This > would be reasonably convenient for the ad-hoc testing that this call > serves.) > > Thanks to Roger for diagnosing the Linux kernel bug. > > CC: Roger Pau Monne <roger....@citrix.com> > CC: Jürgen Groß <jgr...@suse.com> > Signed-off-by: Ian Jackson <ian.jack...@eu.citrix.com>
Thanks: Reviewed-by: Roger Pau Monné <roger....@citrix.com> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
