Re: Bugs in multipath scsi in 4.3-rc2

[Christoph Hellwig <hch@lst.de>]

On Wed, Sep 30, 2015 at 03:34:54PM -0700, James Bottomley wrote:
> Perhaps we don't have to be that draconian.  There's no real reason we
> can't autoload asynchronously.  If the module isn't ready by the time we
> come to check the attachment, then it will attach to the device later
> when the module init routine runs.

I don't think this works.  We're attaching just after the request_module
call, so modprobe doesn't really have a chance to finish before we
return.

> Should we do anything to limit the module_request floods?  This will
> likely happen for every LUN of an ALUA system ... there can be hundreds
> of those.

Once the alua module is loaded there won't be any request_module calls.
If you build with device handler support but without ALUA support
you'll get a lot of calls, but that's not any different than probing
for other optional features.

Personally I think we probably should simple build ALUA support into
scsi_mod if SCSI_DH is selected, as that's part of the standard and
supported by any modern multi pathing device.