Re: [PATCH v2] block: fix peeking requests during PM

On Mon, Oct 23, 2017 at 06:43:16PM +0800, Ming Lei wrote:

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

quoted

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.

I thought I stated that the issue is more theoretical, and the
real reason is to refactor this code for later additions.

Seems like that was only in the cover letter of the previous version,
though.