Commit b4606f21 authored Dec 01, 2009 by Ian Campbell Committed by Jeremy Fitzhardinge Dec 03, 2009

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>

parent 65f63384

drivers/xen/manage.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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