[096/151] xen: explicitly create/destroy stop_machine workqueues outside suspend/resume region.

Greg KH
2009-12-17T04:27:11Z

From: Ian Campbell <ian.campbell@citrix.com>

commit b4606f2165153833247823e8c04c5e88cb3d298b upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/xen/manage.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

--- 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;
}