[PATCH] xen: resume console a bit later

[PATCH] xen: resume console a bit later

[David Vrabel]

Calling xen_console_resume() in xen_suspend() causes a (harmless)
warning because it calls a function that might sleep.

Resuming the console after the stop_machine() call returns avoids this
warning.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/xen/manage.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index c3667b2..5f1e1f3 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -88,7 +88,6 @@ static int xen_suspend(void *data)
 
 	if (!si->cancelled) {
 		xen_irq_resume();
-		xen_console_resume();
 		xen_timer_resume();
 	}
 
@@ -135,6 +134,10 @@ static void do_suspend(void)
 
 	err = stop_machine(xen_suspend, &si, cpumask_of(0));
 
+	/* Resume console as early as possible. */
+	if (!si.cancelled)
+		xen_console_resume();
+
 	raw_notifier_call_chain(&xen_resume_notifier, 0, NULL);
 
 	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
-- 
1.7.10.4

Re: [PATCH] xen: resume console a bit later

[Boris Ostrovsky]

On 07/02/2014 12:35 PM, David Vrabel wrote:
> Calling xen_console_resume() in xen_suspend() causes a (harmless)
> warning because it calls a function that might sleep.
>
> Resuming the console after the stop_machine() call returns avoids this
> warning.
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>


> ---
>   drivers/xen/manage.c |    5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index c3667b2..5f1e1f3 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -88,7 +88,6 @@ static int xen_suspend(void *data)
>   
>   	if (!si->cancelled) {
>   		xen_irq_resume();
> -		xen_console_resume();
>   		xen_timer_resume();
>   	}
>   
> @@ -135,6 +134,10 @@ static void do_suspend(void)
>   
>   	err = stop_machine(xen_suspend, &si, cpumask_of(0));
>   
> +	/* Resume console as early as possible. */
> +	if (!si.cancelled)
> +		xen_console_resume();
> +
>   	raw_notifier_call_chain(&xen_resume_notifier, 0, NULL);
>   
>   	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);

Re: [PATCH] xen: resume console a bit later

[David Vrabel]

On 02/07/14 17:58, Boris Ostrovsky wrote:
> On 07/02/2014 12:35 PM, David Vrabel wrote:
>> Calling xen_console_resume() in xen_suspend() causes a (harmless)
>> warning because it calls a function that might sleep.

It occurs to me that this warning isn't harmless.  Whilst the device
power management will ensure no driver is playing with irqs, a userspace
process might be using the evtchn device.

I've updated the commit message to:

    xen/manage: fix potential deadlock when resuming the console

    Calling xen_console_resume() in xen_suspend() causes a warning
    because it locks irq_mapping_update_lock (a mutex) and this may
    sleep.  If a userspace process is using the evtchn device then
    this mutex may be locked at the point of the stop_machine() call and
    xen_console_resume() would then deadlock.

    Resuming the console after stop_machine() returns avoids this
    deadlock.

And tagged for stable and applied to stable/for-linus-3.6

David