linux-kernel - Re: [RFC PATCH] percpu system call: fast userspace percpu critical sections

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Date:	Sat, 23 May 2015 13:11:33 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
	Ben Maurer <bmaurer@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] percpu system call: fast userspace percpu critical sections

On Thu, May 21, 2015 at 7:44 AM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
> Expose a new system call allowing userspace threads to register
> a TLS area used as an ABI between the kernel and userspace to
> share information required to create efficient per-cpu critical
> sections in user-space.

Not a way in hell.

You do user accesses from preempt notifiers.

That's so ludicrously broken that it's not even funny.

This patch needs to die, and never *ever* be resurrected. Put a stake
in it, and bury it 6ft deep.

               Linus
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