• Ian Campbell's avatar
    xen: netback: read hotplug script once at start of day. · 31a41898
    Ian Campbell authored
    When we come to tear things down in netback_remove() and generate the
    uevent it is possible that the xenstore directory has already been
    removed (details below).
    
    In such cases netback_uevent() won't be able to read the hotplug
    script and will write a xenstore error node.
    
    A recent change to the hypervisor exposed this race such that we now
    sometimes lose it (where apparently we didn't ever before).
    
    Instead read the hotplug script configuration during setup and use it
    for the lifetime of the backend device.
    
    The apparently more obvious fix of moving the transition to
    state=Closed in netback_remove() to after the uevent does not work
    because it is possible that we are already in state=Closed (in
    reaction to the guest having disconnected as it shutdown). Being
    already in Closed means the toolstack is at liberty to start tearing
    down the xenstore directories. In principal it might be possible to
    arrange to unregister the device sooner (e.g on transition to Closing)
    such that xenstore would still be there but this state machine is
    fragile and prone to anger...
    
    A modern Xen system only relies on the hotplug uevent for driver
    domains, when the backend is in the same domain as the toolstack it
    will run the necessary setup/teardown directly in the correct sequence
    wrt xenstore changes.
    Signed-off-by: default avatarIan Campbell <ian.campbell@citrix.com>
    Acked-by: default avatarWei Liu <wei.liu2@citrix.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    31a41898
xenbus.c 25.8 KB