[Xen-devel] [PATCH V2 2/2] xenbus: defer xenbus frontend resume if xenstored is not running

[Aurelien Chartier <aurelien.chartier@xxxxxxxxxx>]

If the xenbus frontend is running in a domain running xenstored, the device
resume is hanging because it is happening before the process resume. This
patch adds extra logic to the resume code to check if we are the domain
running xenstored and delay the resume if needed.

Signed-off-by: Aurelien Chartier <aurelien.chartier@xxxxxxxxxx>

Changes in v2:
- Instead of bypassing the resume, process it in a workqueue
---
 drivers/xen/xenbus/xenbus_probe.h          |    5 ++++
 drivers/xen/xenbus/xenbus_probe_frontend.c |   34 +++++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.h 
b/drivers/xen/xenbus/xenbus_probe.h
index 146f857..46b384c 100644
--- a/drivers/xen/xenbus/xenbus_probe.h
+++ b/drivers/xen/xenbus/xenbus_probe.h
@@ -47,6 +47,11 @@ struct xen_bus_type {
        struct bus_type bus;
 };
 
+struct xenbus_resume_work {
+       struct work_struct w;
+       struct device *dev;
+};
+
 enum xenstore_init {
        XS_UNKNOWN,
        XS_PV,
diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c 
b/drivers/xen/xenbus/xenbus_probe_frontend.c
index 3159a37..83b83d0 100644
--- a/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -28,6 +28,7 @@
 #include "xenbus_comms.h"
 #include "xenbus_probe.h"
 
+static struct workqueue_struct *xenbus_frontend_resume_wq;
 
 /* device/<type>/<id> => <type>-<id> */
 static int frontend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
@@ -89,9 +90,38 @@ static void backend_changed(struct xenbus_watch *watch,
        xenbus_otherend_changed(watch, vec, len, 1);
 }
 
+static void xenbus_frontend_delayed_resume(struct work_struct *w)
+{
+       struct xenbus_resume_work *resume_work = (struct xenbus_resume_work *) 
w;
+
+       xenbus_dev_resume(dev);
+
+       kfree(w);
+}
+
+static int xenbus_frontend_dev_resume(struct device *dev)
+{
+       /* 
+        * If xenstored is running in that domain, we cannot access the backend
+        * state at the moment, so we need to defer xenbus_dev_resume
+        */
+       if (xen_store_domain == XS_LOCAL) {
+               struct xenbus_resume_work *work =
+                       kmalloc(sizeof(struct xenbus_resume), GFP_KERNEL);
+
+               INIT_WORK((struct work_struct *) work, 
xenbus_frontend_delayed_resume);
+               resume_work->dev = dev;
+               queue_work(xenbus_frontend_resume_wq, (struct work_struct *) 
work)
+
+               return 0;
+       }
+
+       return xenbus_dev_resume(dev);
+}
+
 static const struct dev_pm_ops xenbus_pm_ops = {
        .suspend        = xenbus_dev_suspend,
-       .resume         = xenbus_dev_resume,
+       .resume         = xenbus_frontend_dev_resume,
        .freeze         = xenbus_dev_suspend,
        .thaw           = xenbus_dev_cancel,
        .restore        = xenbus_dev_resume,
@@ -440,6 +470,8 @@ static int __init xenbus_probe_frontend_init(void)
 
        register_xenstore_notifier(&xenstore_notifier);
 
+       xenbus_frontend_resume_wq = create_workqueue("xenbus_frontend_resume");
+
        return 0;
 }
 subsys_initcall(xenbus_probe_frontend_init);
-- 
1.7.10.4


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