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

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Date:   Mon, 13 Nov 2023 15:51:55 +0200
From:   Oleksandr Tyshchenko <olekstysh@...il.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        xen-devel@...ts.xenproject.org, Jan Beulich <jbeulich@...e.com>
Subject: Re: [PATCH 1/7] xen/events: fix delayed eoi list handling



On 16.10.23 09:28, Juergen Gross wrote:


Hello Juergen

> 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>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.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);