[systemd-devel] [PATCH v3 2/3] cxgb4: use module_long_probe_init()

[Luis R. Rodriguez]

On Thu, Aug 14, 2014 at 09:53:21PM +0200, Luis R. Rodriguez wrote:
> On Thu, Aug 14, 2014 at 09:42:49AM -0700, Casey Leedom wrote:
> >   Part of the problem is that the current 
> > architecture has Device Probe happening out of the Module Initialization 
> > when we call pci_register_driver() with our PCI Device ID Table.
> >
> >   Running the Device Probes asynchronously has been discussed but that has 
> > the problem that it's then impossible to return the Device Probe Status.  
> > This is a problem for Driver Fallback and, if the probe fails, we're not 
> > supposed to call the Device Remove function. To make this work, the 
> > synchronous/asynchronous boundary would really need to be up in the PCI 
> > Infrastructure layer so the Device Probe status could be captured in the 
> > normal logic.  This would be a moderately large change there ...
> 
> Some maintainers consider most of the work to get what you need done
> simple, I've tried to explain it ain't so, so glad you provided a bit
> of details here. To be clear its not just about asynch firmware loading,
> you need a bit more work. Can you evaluate using a bus driver?

<-- snip -->

> >   On the whole, I think that introducing these Module Load Timeouts hasn't 
> > been well thought out with respect to the repercussions and I'd be more 
> > inclined to back that out till a well thought out design is developed.  But 
> > I'm here for the discussion.
> 
> The way that the 30 second timeout was introduced as a new driver
> initialization requirement was certainly not ideal specially since
> the respective systemd patch that intended to trigger the SIGKILL on
> kmod module loading only took effect once kernel commit 786235ee
> went in about a year later, and since the original systemd commit
> was only addressing asynchronous firmware loading as a possible
> issue that drivers may need to fix. The cxgb4 driver is a good
> example that needs quite a bit of more work. Regardless systemd
> folks are right -- but again, having this be introduced as a new
> requirement that otherwise simply kills drivers seems a bit too
> aggressive specially if its killing boot on some systems due to
> delays on storage drivers. What's done is done -- and we need to
> move on. We already reviewed twice now reverting 786235ee and that
> won't happen, as a compromise we're looking for an easy agreeable
> general driver work around that would both circumvent the issue
> and let us easily grep for broken drivers. The deferred probe trick
> was the first approach and this series addresses the more agreeable
> solution. This 2 line patch then is what we are looking as work
> around until your driver gets properly fixed.
> 
> Apart from these kernel changes there are systemd changes we've
> looked at modifying, Hannes' patch 9719859c07a, now merged upstream on
> systemd lets you override the timeout value through the kernel command
> line. This will only help for all systems if you use a high enough
> large timeout value, or on a case by case basis for each system.
> I recently proposed replacing a kill for a warn only for udev
> kmod built in commands, that's unacceptable for systemd's architecture
> though so the last thing I proposed instead to use *for now* is a
> multiplier for each different type of udev built-in command and
> for kmod we'd use a high enough value, the timeout therefore would
> be really large for module loading for now, but we'd still want to
> collect logs of drivers taking long to probe. That's still being
> discussed [0] but my hope is that with this series and that other
> systemd discussion we'll have covered both areas affected and have
> a good strategy to move forward with this new driver requirement.
> 
> [0] http://comments.gmane.org/gmane.comp.sysutils.systemd.devel/21689

Here's another affected driver:

https://bugzilla.kernel.org/show_bug.cgi?id=59581

pata_marvell, and using the work around in this series should work,
just as the deferred probe work around. Alexander however notes that
the pata_marvell driver is just a simple wrapper and other devices
can act the same way. This can surely be fixed perhaps in libata
but its an example of an old driver and folks not being around to
care much over drivers which are affected.

This driver also uses module_pci_driver() so a module_long_probe_driver()
and respective module_long_probe_pci_driver() would need to be considered
if but easily implemented (sent to Alex to test).

  Luis