linux-kernel - [PATCH 0/3] (Was: sched: start stopper early)

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

Date:	Sat, 10 Oct 2015 20:52:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	heiko.carstens@...ibm.com, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/3] (Was: sched: start stopper early)

To avoid the confusion, this has nothing to do with "stop_machine"
changes we discuss in another thread, but

On 10/09, Oleg Nesterov wrote:
>
> >  	case CPU_ONLINE:
> > +		stop_machine_unpark(cpu);
> >  		/*
> >  		 * At this point a starting CPU has marked itself as online via
> >  		 * set_cpu_online(). But it might not yet have marked itself
> > @@ -5337,7 +5340,7 @@ static int sched_cpu_active(struct notifier_block *nfb,
> >  		 * Thus, fall-through and help the starting CPU along.
> >  		 */
> >  	case CPU_DOWN_FAILED:
> > -		set_cpu_active((long)hcpu, true);
> > +		set_cpu_active(cpu, true);
>
> On a second thought, we can't do this (and your initial change has
> the same problem).
>
> We can not wakeup it before set_cpu_active(). This can lead to the
> same problem fixed by dd9d3843755da95f6 "sched: Fix cpu_active_mask/
> cpu_online_mask race".

OTOH, I don't understand why do we actually need this fix... Or, iow
I don't really understand the cpu_active() checks in select_fallback_rq().

Looks like we have some strange arch/ which has the "unsafe" online &&
!active window, but then it is not clear why it is safe to mark it active
in sched_cpu_active(CPU_ONLINE). Confused.

And I am even more confused by the fact that select_fallback_rq()
checks cpu_active(), but select_task_rq() doesn't. This can't be right
in any case.

Oleg.


 kernel/sched/core.c |   41 +++++++++++++++++++++--------------------
 1 files changed, 21 insertions(+), 20 deletions(-)

--
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/