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

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Date:	Mon, 08 Jun 2015 13:39:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	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>,
	Steven Rostedt <rostedt@...dmis.org>,
	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>,
	Jiri Kosina <jkosina@...e.cz>, 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 Mon, 2015-06-08 at 12:01 +0200, Petr Mladek wrote:

> Just to be sure. Do you suggest to use TASK_IDLE everywhere in
> kthreads or only when the uninterruptible sleep is really needed?

Always, only use INTERRUPTIBLE when you're actually interruptible, that
is you want signals or such muck to terminate your wait.

> IMHO, we should not use TASK_IDLE in freezable kthreads because
> it would break freezing.

How so? The task is IDLE, its not doing anything.

>  Well, we could freezable_schedule() but only
> on locations where it is safe to get freezed. Anyway, we need to
> be careful here.

s/freezed/frozen/

Bah, you made me look at the freezer code, karma reduction for you.

And this is the arch typical freeze point if ever there was one, you're
checking kthread_stop, if we can terminate the kthread, we can certainly
get frozen.

> BTW: What is the preferred way of freezing, please? Is it better
> to end up in the fridge or is it fine to call freezer_do_not_count();
> or set PF_NOFREEZE when it is safe?

freezable_schedule() is fine in this case.
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