linux-kernel - [PATCH 0/2] kthread: kill task_get_live

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Message-ID: <20130311173625.GA13525@redhat.com>
Date:	Mon, 11 Mar 2013 18:36:25 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Namhyung Kim <namhyung@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] kthread: kill task_get_live_kthread()

Hello.

Imho, task_get_live_kthread() is very confusing and unneeded.
2a1d4460 copied get_task_struct() + "vfork_done != NULL" from
kthread_stop(), but only kthread_stop() needs them both.

It needs get_task_struct() because kthread_stop() can be used
when the caller doesn't have a reference but we know that this
thread can't exit itself.

At the same time, if it can exit we do not need get_task_struct()
(the caller must have a reference) but we need to ensure we do not
use to_kthread(NULL) if it has exited.

I think that kthread_park/unpark can simply use to_kthread(), but
this series only removes get_task_struct() and keeps "alive" check.

But the actual reason for this cleanup is that I do not understand
why park/unpark abuse kthread.c.

Thomas, can't we move kthread->parked/cpu to smpboot_thread_data
and move all this code into kernel/smpboot.c? Just for example,
why kthread() does __kthread_parkme() ? smpboot_thread_fn() can do
this at the start.

Or this would be wrong/undesirable by some reason?

Oleg.

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