linux-kernel - Re: [PATCH v1 11/15] arm/futex: UP futex_atomic_op

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Message-ID: <20150512190014.GD25464@linutronix.de>
Date:	Tue, 12 May 2015 21:00:14 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	yang.shi@...driver.com, benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
	tglx@...utronix.de, David.Laight@...LAB.COM, hughd@...gle.com,
	hocko@...e.cz, ralf@...ux-mips.org, herbert@...dor.apana.org.au,
	linux@....linux.org.uk, airlied@...ux.ie, daniel.vetter@...el.com,
	linux-mm@...ck.org, linux-arch@...r.kernel.org,
	peterz@...radead.org
Subject: Re: [PATCH v1 11/15] arm/futex: UP futex_atomic_op_inuser() relies
 on disabled preemption

* David Hildenbrand | 2015-05-11 17:52:16 [+0200]:

>The !CONFIG_SMP implementation of futex_atomic_op_inuser() seems to rely
>on disabled preemption to guarantee mutual exclusion.

Yes, this is what the code looks like. It is more the requirement for
ldrex/strex opcodes which are ARMv6+ and so is SMP support (here).
Documentation wise you could replace CONFIG_SMP by 
     __LINUX_ARM_ARCH__ >= 6
in a later patch if you like. This would be more in-sync with
arch/arm/include/asm/cmpxchg.h :)

Sebastian
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