linux-kernel - Re: RFC: SysRq nice-all-RT-tasks is broken

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Message-ID: <20170308124654.10e598f2@gandalf.local.home>
Date:   Wed, 8 Mar 2017 12:46:54 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...l.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: RFC: SysRq nice-all-RT-tasks is broken

On Wed, 8 Mar 2017 12:40:12 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> I wonder if we should just have a special flag sent by that sysrq
> trigger. Since it is causing all tasks to go "nice" there's no need to
> do the pi chain walk in __sched_setscheduler().

Hah, there already is a flag!

Laurent, can you test this patch:

-- Steve

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b31fc0..7292fa9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4129,8 +4129,8 @@ static int __sched_setscheduler(struct task_struct *p,
 	int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
 	struct rq *rq;
 
-	/* May grab non-irq protected spin_locks: */
-	BUG_ON(in_interrupt());
+	/* The pi code expects interrupts enabled */
+	BUG_ON(pi && in_interrupt());
 recheck:
 	/* Double check policy once rq lock held: */
 	if (policy < 0) {