linux-kernel - Re: [PATCH v3 REPOST] sched: Remove a preempt-disable section in rt_mutex

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20251128100659.GY4067720@noisy.programming.kicks-ass.net>
Date: Fri, 28 Nov 2025 11:06:59 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH v3 REPOST] sched: Remove a preempt-disable section in
 rt_mutex_setprio()

On Thu, Nov 27, 2025 at 04:55:29PM +0100, Sebastian Andrzej Siewior wrote:
> rt_mutex_setprio() has only one caller: rt_mutex_adjust_prio(). It
> expects that task_struct::pi_lock and rt_mutex_base::wait_lock are held.
> Both locks are raw_spinlock_t and are acquired with disabled interrupts.
> 
> Nevertheless rt_mutex_setprio() disables preemption while invoking
> __balance_callbacks() and raw_spin_rq_unlock(). Even if one of the
> balance callbacks unlocks the rq then it must not enable interrupts
> because rt_mutex_base::wait_lock is still locked.
> Therefore interrupts should remain disabled and disabling preemption is
> not needed.
> 
> Commit 4c9a4bc89a9cc ("sched: Allow balance callbacks for check_class_changed()")
> adds a preempt-disable section to rt_mutex_setprio() and
> __sched_setscheduler(). In __sched_setscheduler() the preemption is
> disabled before rq is unlocked and interrupts enabled but I don't see
> why it makes a difference in rt_mutex_setprio().
> 
> Remove the preempt_disable() section from rt_mutex_setprio().
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Thanks!