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

[Jan Beulich <jbeulich@xxxxxxxx>]

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?

Jan