linux-kernel - Re: [RFC] Thread Migration 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-next>] [day] [month] [year] [list]

Date:	Fri, 6 Jul 2007 10:02:57 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] Thread Migration Preemption

Mathieu Desnoyers wrote:
>
> This patch adds the ability to protect critical sections from migration to
> another CPU without disabling preemption.
>
> Typical use:
>
> migration_disable();
> local_inc(&__get_cpu_var(&my_local_t_var));
> migration_enable();
>
> --- linux-2.6-lttng.orig/kernel/sched.c	2007-07-05 16:28:15.000000000 -0400
> +++ linux-2.6-lttng/kernel/sched.c	2007-07-05 16:53:24.000000000 -0400
> @@ -1996,6 +1996,7 @@
>  	 * 1) running (obviously), or
>  	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
>  	 * 3) are cache-hot on their current CPU.
> +	 * 4) migration preemption is non 0 for this non running task.
>  	 */
>  	if (!cpu_isset(this_cpu, p->cpus_allowed))
>  		return 0;
> @@ -2003,6 +2004,8 @@
>
>  	if (task_running(rq, p))
>  		return 0;
> +	if (task_thread_info(p)->migration_count)
> +		return 0;

Question: This means that the task could be preempted, but can't sleep, yes?

Because try_to_wake_up() can change ->cpu. Shouldn't might_sleep() check
->migration_count then? Or we can change try_to_wake_up().

What if the task does copy_process() under migration_disable() ? Child
gets a copy of ->migration_count.

Also, cpu_down() still can migrate this task to another CPU.

Oleg.

-
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/