lkml.org 
[lkml]   [2021]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.19 53/57] xen-netback: Check for hotplug-status existence before watching
    Date
    From: Michael Brown <mbrown@fensystems.co.uk>

    [ Upstream commit 2afeec08ab5c86ae21952151f726bfe184f6b23d ]

    The logic in connect() is currently written with the assumption that
    xenbus_watch_pathfmt() will return an error for a node that does not
    exist. This assumption is incorrect: xenstore does allow a watch to
    be registered for a nonexistent node (and will send notifications
    should the node be subsequently created).

    As of commit 1f2565780 ("xen-netback: remove 'hotplug-status' once it
    has served its purpose"), this leads to a failure when a domU
    transitions into XenbusStateConnected more than once. On the first
    domU transition into Connected state, the "hotplug-status" node will
    be deleted by the hotplug_status_changed() callback in dom0. On the
    second or subsequent domU transition into Connected state, the
    hotplug_status_changed() callback will therefore never be invoked, and
    so the backend will remain stuck in InitWait.

    This failure prevents scenarios such as reloading the xen-netfront
    module within a domU, or booting a domU via iPXE. There is
    unfortunately no way for the domU to work around this dom0 bug.

    Fix by explicitly checking for existence of the "hotplug-status" node,
    thereby creating the behaviour that was previously assumed to exist.

    Signed-off-by: Michael Brown <mbrown@fensystems.co.uk>
    Reviewed-by: Paul Durrant <paul@xen.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/net/xen-netback/xenbus.c | 12 ++++++++----
    1 file changed, 8 insertions(+), 4 deletions(-)

    diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
    index 107bbd4ae825..78c56149559c 100644
    --- a/drivers/net/xen-netback/xenbus.c
    +++ b/drivers/net/xen-netback/xenbus.c
    @@ -1043,11 +1043,15 @@ static void connect(struct backend_info *be)
    xenvif_carrier_on(be->vif);

    unregister_hotplug_status_watch(be);
    - err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch, NULL,
    - hotplug_status_changed,
    - "%s/%s", dev->nodename, "hotplug-status");
    - if (!err)
    + if (xenbus_exists(XBT_NIL, dev->nodename, "hotplug-status")) {
    + err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
    + NULL, hotplug_status_changed,
    + "%s/%s", dev->nodename,
    + "hotplug-status");
    + if (err)
    + goto err;
    be->have_hotplug_status_watch = 1;
    + }

    netif_tx_wake_all_queues(be->vif->dev);

    --
    2.30.2


    \
     
     \ /
      Last update: 2021-04-26 09:46    [W:5.194 / U:0.792 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site