linux-kernel - Re: [patch V3 09/12] rseq: Reset slice extension when scheduled

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Message-ID: <18282cb6-f343-4703-a022-dc40edd1c6f6@efficios.com>
Date: Fri, 31 Oct 2025 16:03:26 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Jonathan Corbet <corbet@....net>,
 Prakash Sangappa <prakash.sangappa@...cle.com>,
 Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
 K Prateek Nayak <kprateek.nayak@....com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org
Subject: Re: [patch V3 09/12] rseq: Reset slice extension when scheduled

On 2025-10-29 09:22, Thomas Gleixner wrote:
> When a time slice extension was granted in the need_resched() check on exit
> to user space, the task can still be scheduled out in one of the other
> pending work items. When it gets scheduled back in, and need_resched() is
> not set, then the stale grant would be preserved, which is just wrong.
> 
> RSEQ already keeps track of that and sets TIF_RSEQ, which invokes the
> critical section and ID update mechanisms.
> 
> Utilize them and clear the user space slice control member of struct rseq
> unconditionally within the existing user access sections. That's just an
> unconditional store more in that path.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com