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From: Oleg Nesterov <oleg@redhat.com>
To: Will Deacon <will.deacon@arm.com>
Cc: paulmck@linux.vnet.ibm.com, peterz@infradead.org,
	torvalds@linux-foundation.org, benh@kernel.crashing.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: Behaviour of smp_mb__{before,after}_spin* and acquire/release
Date: Tue, 13 Jan 2015 19:45:10 +0100	[thread overview]
Message-ID: <20150113184510.GA31525@redhat.com> (raw)
In-Reply-To: <20150113163353.GE31784@arm.com>

On 01/13, Will Deacon wrote:
>
>   1. Does smp_mb__before_spinlock actually have to order prior loads
>      against later loads and stores? Documentation/memory-barriers.txt
>      says it does, but that doesn't match the comment

The comment says that smp_mb__before_spinlock() + spin_lock() should
only serialize STOREs with LOADs. This is because it was added to ensure
that the setting of condition can't race with ->state check in ttwu().

But since we use wmb() it obviously serializes STOREs with STORES. I do
not know if this should be documented, but we already have another user
which seems to rely on this fact: set_tlb_flush_pending().

As for "prior loads", this doesn't look true...

Oleg.


  reply	other threads:[~2015-01-13 18:46 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-13 16:33 Will Deacon
2015-01-13 18:45 ` Oleg Nesterov [this message]
2015-01-14 11:31   ` Will Deacon
2015-01-20  3:40     ` Paul E. McKenney
2015-01-20 10:43       ` Will Deacon
2015-01-20  9:34 ` Peter Zijlstra
2015-01-20 10:38   ` Will Deacon
2015-01-20 21:35   ` Paul E. McKenney
2015-01-21 13:56     ` Will Deacon
2015-01-23 14:08     ` Will Deacon
2015-01-23 21:21       ` Paul E. McKenney

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