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== Comment: #0 - Hendrik Brueckner - 2016-03-15 06:29:41 ==
The kernel configuration, CONFIG_SCSI_SCAN_ASYNC, is still set.  Please do not enable this kernel configuration for s390x.

Background why you shall disable this option:

The long-term default "sync" is probably well-tested.  Experiences with async
are rare.  To be more frank here, sync is also used by other Linux distributions
on z.  For s390, the defconfig as well as our other upstream kernel
configurations have or will have this being set to sync (again).

Apart from testing, the reason why I suggest to change this setting goes back
to a talk with the zfcp device driver maintainer.  I stumbled over this
setting as trying out FCP devices on a Debian s390 system.  Tools are
expecting that attached LUNs to an FCP device should be synchronously, that
means, the requests should be synchronously processed by the FCP device and
the SCSI layer on top.  Asynchronous processing might cause problems in tools
that expect synchronous behavior.  Further, asynchronous handling makes it
more harder to wait for the SCSI device becomes available (if it exists at
all).  Thus, tools have to actively wait for something to happen... and the
worst thing is, that there is no tooling at all that waits for asynchronous
processing to become completed (udevadm settle is useless here as there are
no uevent for LUN attachment requests).

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Andy Whitcroft (apw)
         Status: New


** Tags: architecture-s39064 bugnameltc-139033 severity-critical targetmilestone-inin1604
-- 
s390/kconfig: do not set CONFIG_SCSI_SCAN_ASYNC
https://bugs.launchpad.net/bugs/1557692
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