linux-kernel - Re: [PATCH 08/16] freezer: use dedicated lock instead of task

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Date:	Sun, 28 Aug 2011 19:51:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	rjw@...k.pl, paul@...lmenage.org, linux-kernel@...r.kernel.org,
	arnd@...db.de
Subject: Re: [PATCH 08/16] freezer: use dedicated lock instead of
	task_lock() + memory barrier

On 08/19, Tejun Heo wrote:
>
> it's by no means a
> hot path and the priority is staying unintrusive and safe.  This patch
> makes it simply use a dedicated lock

Agreed. but could you explain why it should be irq-safe? This is not
clear from the changelog.

> +	if (!(current->flags & PF_NOFREEZE))
> +		current->flags |= PF_FROZEN;

it is not clear why do we check PF_NOFREEZE... but OK, iiuc you
remove this check later anyway.

Off-topic, but fake_signal_wake_up() is not safe if the caller
try_to_freeze_cgroup(). Unlike try_to_freeze_tasks() (which holds
tasklist) we can race with the exiting thread, ->sighand can be
NULL.

Oleg.

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