Re: [PATCH] xen: Fix XenStore initialisation for XS_LOCAL

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 1/26/21 12:01 PM, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> 
> In commit 3499ba8198ca ("xen: Fix event channel callback via INTX/GSI")
> I reworked the triggering of xenbus_probe().
> 
> I tried to simplify things by taking out the workqueue based startup
> triggered from wake_waiting(); the somewhat poorly named xenbus IRQ
> handler.
> 
> I missed the fact that in the XS_LOCAL case (Dom0 starting its own
> xenstored or xenstore-stubdom, which happens after the kernel is booted
> completely), that IRQ-based trigger is still actually needed.
> 
> So... put it back, except more cleanly. By just spawning a xenbus_probe
> thread which waits on xb_waitq and runs the probe the first time it
> gets woken, just as the workqueue-based hack did.
> 
> This is actually a nicer approach for *all* the back ends with different
> interrupt methods, and we can switch them all over to that without the
> complex conditions for when to trigger it. But not in -rc6. This is
> the minimal fix for the regression, although it's a step in the right
> direction instead of doing a partial revert and actually putting the
> workqueue back. It's also simpler than the workqueue.


Wouldn't the minimal fix be to restore wake_waiting() to its previous 

        if (unlikely(xenstored_ready == 0)) {
                xenstored_ready = 1;
                schedule_work(&probe_work);
        }

(And to avoid changing xenbus_probe()'s signature just create a wrapper)

-boris