linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+55aFxdsYMuUzdEhGThdtDJA+f1jeKn-rEH+Zrxk5=-KnsSRw@mail.gmail.com>
Date:	Sat, 13 Dec 2014 17:35:17 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: frequent lockups in 3.18rc4

On Sat, Dec 13, 2014 at 4:33 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> So does SMP - this_cpu_dec() relies on preemption being disabled.

No. really. It very much does not. Not on x86, not elsewhere. It's
part of the whole point of "this_cpu_p()". They are preemption and
interrupt safe.

It's the "__this_cpu_op()" ones that need external protection.

                     Linus
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