linux-kernel - [PATCH v2] sched: Fix broken setscheduler()

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

Message-ID: <20140306120438.638bfe94@gandalf.local.home>
Date:	Thu, 6 Mar 2014 12:04:38 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v2] sched: Fix broken setscheduler()

On Thu, 6 Mar 2014 13:20:40 +0100
Juri Lelli <juri.lelli@...il.com> wrote:

> Yes. I think you can go with
> 
>  p->prio = p->normal_prio
> 
> and save a few checks in rt_mutex_getprio().
> 

You're right! Thanks.

-----

I decided to run my tests on linux-next, and my wakeup_rt tracer was
broken. After running a bisect, I found that the problem commit was:

   linux-next commit c365c292d059
   "sched: Consider pi boosting in setscheduler()"

And the reason the wake_rt tracer test was failing, was because it had
no RT task to trace. I first noticed this when running with
sched_switch event and saw that my RT task still had normal SCHED_OTHER
priority. Looking at the problem commit, I found:

 -       p->normal_prio = normal_prio(p);
 -       p->prio = rt_mutex_getprio(p);

With no

 +       p->normal_prio = normal_prio(p);
 +       p->prio = rt_mutex_getprio(p);

Reading what the commit is suppose to do, I realize that the p->prio
can't be set if the task is boosted with a higher prio, but the
p->normal_prio still needs to be set regardless, otherwise, when the
task is deboosted, it wont get the new priority.

The p->prio has to be set before "check_class_changed()" is called,
otherwise the class wont be changed.

Link: http://lkml.kernel.org/r/20140305232931.449eef8c@gandalf.local.home

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/sched/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4600bca..3134756 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3198,6 +3198,7 @@ static void __setscheduler_params(struct task_struct *p,
 	 * getparam()/getattr() don't report silly values for !rt tasks.
 	 */
 	p->rt_priority = attr->sched_priority;
+	p->normal_prio = normal_prio(p);
 	set_load_weight(p);
 }
 
@@ -3207,6 +3208,12 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
 {
 	__setscheduler_params(p, attr);
 
+	/*
+	 * If we get here, there was no pi waiters boosting the
+	 * task. It is safe to use the normal prio.
+	 */
+	p->prio = normal_prio(p);
+
 	if (dl_prio(p->prio))
 		p->sched_class = &dl_sched_class;
 	else if (rt_prio(p->prio))
-- 
1.8.1.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/