linux-kernel - [PATCH 1/7] xen/events: fix delayed eoi list handling

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Date:   Mon, 16 Oct 2023 08:28:25 +0200
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        xen-devel@...ts.xenproject.org, Jan Beulich <jbeulich@...e.com>
Subject: [PATCH 1/7] xen/events: fix delayed eoi list handling

When delaying eoi handling of events, the related elements are queued
into the percpu lateeoi list. In case the list isn't empty, the
elements should be sorted by the time when eoi handling is to happen.

Unfortunately a new element will never be queued at the start of the
list, even if it has a handling time lower than all other list
elements.

Fix that by handling that case the same way as for an empty list.

Fixes: e99502f76271 ("xen/events: defer eoi in case of excessive number of events")
Reported-by: Jan Beulich <jbeulich@...e.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 drivers/xen/events/events_base.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 1b2136fe0fa5..0e458b1c0c8c 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -601,7 +601,9 @@ static void lateeoi_list_add(struct irq_info *info)
 
 	spin_lock_irqsave(&eoi->eoi_list_lock, flags);
 
-	if (list_empty(&eoi->eoi_list)) {
+	elem = list_first_entry_or_null(&eoi->eoi_list, struct irq_info,
+					eoi_list);
+	if (!elem || info->eoi_time < elem->eoi_time) {
 		list_add(&info->eoi_list, &eoi->eoi_list);
 		mod_delayed_work_on(info->eoi_cpu, system_wq,
 				    &eoi->delayed, delay);
-- 
2.35.3