[Xen-devel] [PV-onHVM][linux-2.6.18-xen.hg][PATCH 1/3] Fix kthread_create

[Ben Guthro <bguthro@xxxxxxxxxxxxxxx>]

This patch fixes live migration with PV-on-HVM drivers. 
Without this, the kthread_create of the thread to run xen_suspend hangs 
forever (at least on RHEL4 64bit). 
The comments in the patch explain the problem in more detail.
Signed-off-by: Ben Guthro <bguthro@xxxxxxxxxxxxxxx>
Signed-off-by: Robert Phillips <rphillips@xxxxxxxxxxxxxxx>

diff -r 21dbc5f5a258 drivers/xen/core/reboot.c
--- a/drivers/xen/core/reboot.c Wed Jun 27 11:54:32 2007 -0400
+++ b/drivers/xen/core/reboot.c Wed Jun 27 11:54:43 2007 -0400
@@ -78,6 +78,10 @@ static int kthread_create_on_cpu(int (*f
                                 int cpu)
 {
        struct task_struct *p;
+        /* NB: kthread_create uses the workqueue and
+         * blocks until the new thread is running,
+         * so it will deadlock if called from the worker thread!
+         */
        p = kthread_create(f, arg, name);
        if (IS_ERR(p))
                return PTR_ERR(p);
@@ -94,7 +98,10 @@ static void __shutdown_handler(void *unu
                err = kernel_thread(shutdown_process, NULL,
                                    CLONE_FS | CLONE_FILES);
        else
-               err = kthread_create_on_cpu(xen_suspend, NULL, "suspend", 0);
+                /* It is safe to call kernel_thread from this
+                 * (the worker) thread. */
+                err = kernel_thread(xen_suspend, NULL,
+                                    CLONE_FS | CLONE_FILES);
 
        if (err < 0) {
                printk(KERN_WARNING "Error creating shutdown process (%d): "
@@ -138,8 +145,17 @@ static void shutdown_handler(struct xenb
                shutting_down = SHUTDOWN_POWEROFF;
        else if (strcmp(str, "reboot") == 0)
                ctrl_alt_del();
-       else if (strcmp(str, "suspend") == 0)
+       else if (strcmp(str, "suspend") == 0) {
                shutting_down = SHUTDOWN_SUSPEND;
+                /* Create new thread from this (the xenwatch) thread.
+                 * If called from worker thread, we'll deadlock. */
+               err = kthread_create_on_cpu(xen_suspend, NULL, "suspend", 0);
+                if (err < 0) {
+                    printk(KERN_WARNING "Error creating shutdown process (%d): 
"
+                           "retrying...\n", -err);
+                    schedule_delayed_work(&shutdown_work, HZ/2);
+                }
+        }
        else if (strcmp(str, "halt") == 0)
                shutting_down = SHUTDOWN_HALT;
        else {
@@ -147,7 +163,8 @@ static void shutdown_handler(struct xenb
                shutting_down = SHUTDOWN_INVALID;
        }
 
-       if (shutting_down != SHUTDOWN_INVALID)
+       if (shutting_down != SHUTDOWN_INVALID &&
+            shutting_down != SHUTDOWN_SUSPEND)
                schedule_work(&shutdown_work);
 
        kfree(str);
diff -r 21dbc5f5a258 drivers/xen/xenbus/xenbus_dev.c
--- a/drivers/xen/xenbus/xenbus_dev.c   Wed Jun 27 11:54:32 2007 -0400
+++ b/drivers/xen/xenbus/xenbus_dev.c   Wed Jun 27 11:54:35 2007 -0400
@@ -386,7 +386,7 @@ static unsigned int xenbus_dev_poll(stru
        return 0;
 }
 
-static const struct file_operations xenbus_dev_file_ops = {
+static struct file_operations xenbus_dev_file_ops = {
        .read = xenbus_dev_read,
        .write = xenbus_dev_write,
        .open = xenbus_dev_open,

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