On Fri, Oct 20, 2017 at 04:45:23PM +0200, Christoph Hellwig wrote:

We need to look for an active PM request until the next softbarrier
instead of looking for the first non-PM request.  Otherwise any cause
of request reordering might starve the PM request(s).

Hi Christoph,

Could you share us how the starve is caused? Looks all PM
request is run via scsi_execute(), and the caller is always
waiting for the completion of PM request.

Especially PM request is run after SCSI device is in quiesce
state, during that time, no normal(non-preempt) request can
enter queue after the making quiesce safe patchset is merged.

--
Ming