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FAILED: patch "[PATCH] xen/events: reset active flag for lateeoi events later" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message Jun 27, 2021

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Stable branch Xen hypervisor interface
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The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3de218ff39b9e3f0d453fe3154f12a174de44b25 Mon Sep 17 00:00:00 2001
From: Juergen Gross <[email protected]>
Date: Wed, 23 Jun 2021 15:09:13 +0200
Subject: [PATCH] xen/events: reset active flag for lateeoi events later

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.

Cc [email protected]
Reported-by Julien Grall <[email protected]>
Fixes b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time")
Tested-by Julien Grall <[email protected]>
Signed-off-by Juergen Gross <[email protected]>
Reviewed-by Boris Ostrovsky <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Juergen Gross <[email protected]>
drivers/xen/events/events_base.c +10 -1
index 7bbfd58958bc..d7e361fb0548 100644
@@ -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);
 	}
 }