Date: Tue, 12 May 2015 21:00:14 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: David Hildenbrand <dahi@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, yang.shi@windriver.com,
        benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org,
        heiko.carstens@de.ibm.com, schwidefsky@de.ibm.com,
        borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de,
        David.Laight@ACULAB.COM, hughd@google.com, hocko@suse.cz,
        ralf@linux-mips.org, herbert@gondor.apana.org.au,
        linux@arm.linux.org.uk, airlied@linux.ie, daniel.vetter@intel.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org, peterz@infradead.org
Subject: Re: [PATCH v1 11/15] arm/futex: UP futex_atomic_op_inuser() relies
 on disabled preemption
Message-ID: <20150512190014.GD25464@linutronix.de>
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* 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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