Re: [PATCH] cxenstored: wait until after reset to notify dom0less domains

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 17 Oct 2023, Jan Beulich wrote:
> 
> On 14.10.2023 01:06, Stefano Stabellini wrote:
> > From: George Dunlap <george.dunlap@xxxxxxxxx>
> > 
> > Commit fc2b57c9a ("xenstored: send an evtchn notification on
> > introduce_domain") introduced the sending of an event channel to the
> > guest when first introduced, so that dom0less domains waiting for the
> > connection would know that xenstore was ready to use.
> > 
> > Unfortunately, it was introduced in introduce_domain(), which 1) is
> > called by other functions, where such functionality is unneeded, and
> > 2) after the main XS_INTRODUCE call, calls domain_conn_reset().  This
> > introduces a race condition, whereby if xenstored is delayed, a domain
> > can wake up, send messages to the buffer, only to have them deleted by
> > xenstore before finishing its processing of the XS_INTRODUCE message.
> > 
> > Move the connect-and-notfy call into do_introduce() instead, after the
> > domain_conn_rest(); predicated on the state being in the
> > XENSTORE_RECONNECT state.
> > 
> > (We don't need to check for "restoring", since that value is always
> > passed as "false" from do_domain_introduce()).
> > 
> > Also take the opportunity to add a missing wmb barrier after resetting
> > the indexes of the ring in domain_conn_reset.
> > 
> > This change will also remove an extra event channel notification for
> > dom0 (because the notification is now done by do_introduce which is not
> > called for dom0.) The extra dom0 event channel notification was only
> > introduced by fc2b57c9a and was never present before. It is not needed
> > because dom0 is the one to tell xenstored the connection parameters, so
> > dom0 has to know that the ring page is setup correctly by the time
> > xenstored starts looking at it. It is dom0 that performs the ring page
> > init.
> > 
> > Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxx>
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> 
> Should this have had a Fixes: tag thus marking it to pick up for
> backport?

Sorry this was committed already