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

On 26.01.21 22:36, Boris Ostrovsky wrote:

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

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;

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

David and I had a longer chat on IRC regarding this fix.

The long term idea is to have just his current thread based variant
for all cases calling xenbus_probe() (so no call of xenbus_probe() at
any other place).

We agreed that this approach would be too risky now, but we wanted to
go in the right direction with the current fix. This is the outcome.


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