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[Bug 1557692] Re: s390/kconfig: do not set CONFIG_SCSI_SCAN_ASYNC


As far as I can see: Fedora, RHEL, z/KVM, Debian, and Ubuntu ship
SCAN_ASYNC on s390x. Thank you for your comments.

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  s390/kconfig: do not set CONFIG_SCSI_SCAN_ASYNC

Status in linux package in Ubuntu:
  Won't Fix

Bug description:
  == 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).

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