linux-kernel - Re: [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on user preemption

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]

Date:	Thu, 06 Sep 2012 19:02:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, patches@...aro.org,
	Alessio Igor Bogani <abogani@...nel.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>
Subject: Re: [PATCH tip/core/rcu 11/26] rcu: Exit RCU extended QS on user
 preemption

On Thu, 2012-08-30 at 14:05 -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@...il.com>
> 
> When exceptions or irq are about to resume userspace, if
> the task needs to be rescheduled, the arch low level code
> calls schedule() directly.
> 
> At that time we may be in extended quiescent state from RCU
> POV: the exception is not anymore protected inside
> rcu_user_exit() - rcu_user_enter() and the irq has called
> rcu_irq_exit() already.
> 
> Create a new API schedule_user() that calls schedule() inside
> rcu_user_exit()-rcu_user_enter() in order to protect it. Archs
> will need to rely on it now to implement user preemption safely.

> ---
>  kernel/sched/core.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0bd599b..e841dfc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3463,6 +3463,13 @@ asmlinkage void __sched schedule(void)
>  }
>  EXPORT_SYMBOL(schedule);
>  
> +asmlinkage void __sched schedule_user(void)
> +{
> +	rcu_user_exit();
> +	schedule();
> +	rcu_user_enter();
> +}


OK, so colour me unconvinced.. why are we doing this?

Typically when we call schedule nr_running != 1 (we need current to be
running and a possible target to switch to).

So I'd prefer to simply have schedule() disable all this adaptive tick
nonsense and leave it at that.
--
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/