[PATCH] xen/events: reset active flag for lateeoi events later

[PATCH] xen/events: reset active flag for lateeoi events later

[Juergen Gross]

In order to avoid a race condition for user events when changing
cpu affinity reset the active flag only when EOI-ing the event.

This is working fine as all user events are lateeoi events. Note that
lateeoi_ack_mask_dynirq() is not modified as there is no explicit call
to xen_irq_lateeoi() expected later.

Reported-by: Julien Grall <julien@xen.org>
Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
Tested-by: Julien Grall <julien@xen.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/xen/events/events_base.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 7bbfd58958bc..d7e361fb0548 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -642,6 +642,9 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious)
 	}
 
 	info->eoi_time = 0;
+
+	/* is_active hasn't been reset yet, do it now. */
+	smp_store_release(&info->is_active, 0);
 	do_unmask(info, EVT_MASK_REASON_EOI_PENDING);
 }
 
@@ -811,6 +814,7 @@ static void xen_evtchn_close(evtchn_port_t port)
 		BUG();
 }
 
+/* Not called for lateeoi events. */
 static void event_handler_exit(struct irq_info *info)
 {
 	smp_store_release(&info->is_active, 0);
@@ -1883,7 +1887,12 @@ static void lateeoi_ack_dynirq(struct irq_data *data)
 
 	if (VALID_EVTCHN(evtchn)) {
 		do_mask(info, EVT_MASK_REASON_EOI_PENDING);
-		event_handler_exit(info);
+		/*
+		 * Don't call event_handler_exit().
+		 * Need to keep is_active non-zero in order to ignore re-raised
+		 * events after cpu affinity changes while a lateeoi is pending.
+		 */
+		clear_evtchn(evtchn);
 	}
 }
 
-- 
2.26.2

Re: [PATCH] xen/events: reset active flag for lateeoi events later

[Boris Ostrovsky]

On 6/23/21 9:09 AM, Juergen Gross wrote:
> In order to avoid a race condition for user events when changing
> cpu affinity reset the active flag only when EOI-ing the event.
>
> This is working fine as all user events are lateeoi events. Note that
> lateeoi_ack_mask_dynirq() is not modified as there is no explicit call
> to xen_irq_lateeoi() expected later.
>
> Reported-by: Julien Grall <julien@xen.org>
> Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
> Tested-by: Julien Grall <julien@xen.org>
> Signed-off-by: Juergen Gross <jgross@suse.com>


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

Re: [PATCH] xen/events: reset active flag for lateeoi events later

[Ross Lagerwall]

On 2021-06-23 14:09, Juergen Gross wrote:
> In order to avoid a race condition for user events when changing
> cpu affinity reset the active flag only when EOI-ing the event.
> 
> This is working fine as all user events are lateeoi events. Note that
> lateeoi_ack_mask_dynirq() is not modified as there is no explicit call
> to xen_irq_lateeoi() expected later.
> 
> Reported-by: Julien Grall <julien@xen.org>
> Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
> Tested-by: Julien Grall <julien@xen.org>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---

Hi Juergen,

Are you planning on backporting this fix to releases <= 5.10?

I think the fix may need some minor adjustment to make it work after
"xen/events: fix setting irq affinity" since both lateeoi_ack_dynirq()
and lateeoi_mask_ack_dynirq() were adjusted to call ack_dynirq().

Thanks,
Ross

Re: [PATCH] xen/events: reset active flag for lateeoi events later

[Juergen Gross]

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On 05.07.21 11:00, Ross Lagerwall wrote:
> On 2021-06-23 14:09, Juergen Gross wrote:
>> In order to avoid a race condition for user events when changing
>> cpu affinity reset the active flag only when EOI-ing the event.
>>
>> This is working fine as all user events are lateeoi events. Note that
>> lateeoi_ack_mask_dynirq() is not modified as there is no explicit call
>> to xen_irq_lateeoi() expected later.
>>
>> Reported-by: Julien Grall <julien@xen.org>
>> Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
>> Tested-by: Julien Grall <julien@xen.org>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
> 
> Hi Juergen,
> 
> Are you planning on backporting this fix to releases <= 5.10?

It is on my todo list. :-)


Juergen

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