From: Sebastian Andrzej Siewior Date: Thu, 27 Nov 2025 15:55:29 +0000 (+0100) Subject: sched/rt: Remove a preempt-disable section in rt_mutex_setprio() X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=22abd832776b1317ae4c3f8a097c8b71bf83fb38;p=thirdparty%2Fkernel%2Flinux.git sched/rt: Remove a preempt-disable section in rt_mutex_setprio() 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 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://patch.msgid.link/20251127155529.t_sTatE4@linutronix.de --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1711e9e50100..ee7dfbf01792 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7352,15 +7352,12 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task) p->prio = prio; } out_unlock: - /* Avoid rq from going away on us: */ - preempt_disable(); + /* Caller holds task_struct::pi_lock, IRQs are still disabled */ rq_unpin_lock(rq, &rf); __balance_callbacks(rq); rq_repin_lock(rq, &rf); __task_rq_unlock(rq, p, &rf); - - preempt_enable(); } #endif /* CONFIG_RT_MUTEXES */