linux-kernel - Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset

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: <20070309235859.GA20093@localdomain>
Date:	Fri, 9 Mar 2007 17:58:59 -0600
From:	Nathan Lynch <ntl@...ox.com>
To:	Cliff Wickman <cpw@....com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset

Hello-

Cliff Wickman wrote:
> This patch would insert a preference to migrate such a task to a cpu within
> its cpuset (and set its cpus_allowed to its cpuset).
> 
> With this patch, migrate the task to:
>  1) to any cpu on the same node as the disabled cpu, which is both online
>     and among that task's cpus_allowed
>  2) to any online cpu within the task's cpuset
>  3) to any cpu which is both online and among that task's cpus_allowed

I think I disagree with this change.

The kernel shouldn't have to be any smarter than it already is about
moving tasks off an offlined cpu.  The only way case 2) can be reached
is if the user has changed a task's cpu affinity.  If the user is
sophisticated enough to manipulate tasks' cpu affinity then they can
arrange to migrate tasks as they see fit before offlining a cpu.

Furthermore:

> --- morton.070123.orig/kernel/sched.c
> +++ morton.070123/kernel/sched.c
> @@ -5170,6 +5170,12 @@ restart:
>  	if (dest_cpu == NR_CPUS)
>  		dest_cpu = any_online_cpu(p->cpus_allowed);
>  
> +	/* try to stay on the same cpuset */
> +	if (dest_cpu == NR_CPUS) {
> +		p->cpus_allowed = cpuset_cpus_allowed(p);
> +		dest_cpu = any_online_cpu(p->cpus_allowed);
> +	}

It's not okay to call cpuset_cpus_allowed in this context -- local
irqs are supposed to have been disabled by the caller of
move_task_off_dead_cpu and cpuset_cpus_allowed acquires a mutex.


-
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/