linux-kernel - Re: [v3.13][v3.14][Regression] kthread: make kthread

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Message-ID: <20140317231814.3249e6d2@alan.etchedpixels.co.uk>
Date:	Mon, 17 Mar 2014 23:18:14 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joseph Salisbury <joseph.salisbury@...onical.com>,
	penguin-kernel@...ove.SAKURA.ne.jp,
	Oleg Nesterov <oleg@...hat.com>, rientjes@...gle.com,
	Linus Torvalds <torvalds@...ux-foundation.org>, tj@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Kernel Team <kernel-team@...ts.ubuntu.com>
Subject: Re: [v3.13][v3.14][Regression] kthread: make kthread_create()
 killable

> Root cause time: it's wrong for the oom-killer to use SIGKILL.  In fact

It has to use SIGKILL anything else might be caught and grow the user
stack a page..

> it's basically always wrong to send signals from in-kernel.  Signals
> are a userspace IPC mechanism and using them in-kernel a) makes it hard
> (or impossible) to distinguish them from userspace-originated signals

Actually signals are a kernel messaging system someone repurposed for IPC.

> and b) permits userspace to produce surprising results in the kernel,
> which I suspect is what we're seeing here.

There is enough information for kernel side code to decide whether a
signal came from kernel or userspace. Then again - it's not clear that it
should ever have to.

Alan
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