linux-kernel - Re: [PATCH 1/3] sched: add sched_task

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Date:	Thu, 19 Feb 2015 22:26:09 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Vojtech Pavlik <vojtech@...e.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched: add sched_task_call()

On Thu, 19 Feb 2015, Josh Poimboeuf wrote:

> How about with a TIF_IN_USERSPACE thread flag?  It could be cleared/set
> right at the border.  Then for running tasks it's as simple as:
> 
> if (test_tsk_thread_flag(task, TIF_IN_USERSPACE))
> 	klp_switch_task_universe(task);

That's in principle what CONTEXT_TRACKING is doing, i.e. the condition 
we'd be interested in would be

	__this_cpu_read(context_tracking.state) == IN_USER

But it has overhead.

-- 
Jiri Kosina
SUSE Labs
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