xen: explicitly create/destroy stop_machine workqueues outside suspend/resume region.

I have observed cases where the implicit stop_machine_destroy() done by
stop_machine() hangs while destroying the workqueues, specifically in
kthread_stop(). This seems to be because timer ticks are not restarted
until after stop_machine() returns.

Fortunately stop_machine provides a facility to pre-create/post-destroy
the workqueues so use this to ensure that workqueues are only destroyed
after everything is really up and running again.

I only actually observed this failure with 2.6.30. It seems that newer
kernels are somehow more robust against doing kthread_stop() without timer
interrupts (I tried some backports of some likely looking candidates but
did not track down the commit which added this robustness). However this
change seems like a reasonable belt&braces thing to do.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 2fb7d39..c499793 100644 (file)
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -79,6 +79,12 @@ static void do_suspend(void)
 
        shutting_down = SHUTDOWN_SUSPEND;
 
+       err = stop_machine_create();
+       if (err) {
+               printk(KERN_ERR "xen suspend: failed to setup stop_machine %d\n", err);
+               goto out;
+       }
+
 #ifdef CONFIG_PREEMPT
        /* If the kernel is preemptible, we need to freeze all the processes
           to prevent them from being in the middle of a pagetable update
@@ -86,7 +92,7 @@ static void do_suspend(void)
        err = freeze_processes();
        if (err) {
                printk(KERN_ERR "xen suspend: freeze failed %d\n", err);
-               goto out;
+               goto out_destroy_sm;
        }
 #endif
 
@@ -129,7 +135,11 @@ out_resume:
 out_thaw:
 #ifdef CONFIG_PREEMPT
        thaw_processes();
+
+out_destroy_sm:
 #endif
+       stop_machine_destroy();
+
 out:
        shutting_down = SHUTDOWN_INVALID;
 }