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Re: [PATCH] xen/sched: rtds: prevent extratime priority_level wraparound
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
- Date: Wed, 1 Apr 2026 13:42:33 +0300
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- Cc: Dario Faggioli <dfaggioli@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Meng Xu <mengxu@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 01 Apr 2026 10:42:54 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Hi Jan,
I have an R-b from Juergen. Should I post another version with "Fixes:"
or it could be added to the commit message during merge?
--
Oleksii
On 31/03/2026 11:10, Jan Beulich wrote:
On 31.03.2026 09:54, Oleksii Moisieiev wrote:
In RTDS, burn_budget() increments priority_level for extratime units
whenever cur_budget is exhausted. As priority_level is unsigned and was
unbounded, it could eventually overflow to 0.
A wrapped value of 0 is the highest RTDS priority, so an extratime unit
could unexpectedly regain top priority and preempt units with active
real-time reservations, violating EDF intent.
Fix this by saturating priority_level at RTDS_MAX_PRIORITY_LEVEL instead
of incrementing unconditionally. Budget refill semantics are unchanged.
Normal behavior is unchanged. Once saturated, priority_level remains at
the lowest priority until the next period update resets it.
Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
From the description, this looks to want to have a Fixes: tag added.
Jan
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