linux-kernel - Re: [RFC PATCH 09/18] kthread: Make it easier to correctly sleep in iterant kthreads

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Message-ID: <alpine.LNX.2.00.1506110625010.12753@pobox.suse.cz>
Date:	Thu, 11 Jun 2015 06:28:28 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Petr Mladek <pmladek@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Anna Schumaker <anna.schumaker@...app.com>,
	linux-nfs@...r.kernel.org, Chris Mason <clm@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...e.de>, Michal Hocko <mhocko@...e.cz>,
	live-patching@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 09/18] kthread: Make it easier to correctly sleep in
 iterant kthreads

On Wed, 10 Jun 2015, Steven Rostedt wrote:

> > Right, and I had not considered that, but it turns out the hung_task
> > detector checks p->state == TASK_UNINTERRUPTIBLE, so TASK_IDLE is indeed
> > safe from that.
> 
> Also, I would assume that TASK_IDLE only makes sense for kernel
> threads, I wonder if we should add an assertion in schedule that
> triggers if a task is scheduling with TASK_IDLE and is not a kernel
> thread (has its own mm?)

For the sake of completnes -- testing for !task_struct->mm is not a 
correct test to find out whether given entity is a kernel thread; kernel 
threads are free to temporarily adopt user struct mm via use_mm() (usually 
for handling AIO on behalf of a particular struct mm).

The correct check is to look at PF_KTHREAD flag in task_struct->flags.

-- 
Jiri Kosina
SUSE Labs
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