linux-kernel - Re: [PATCH] rwsem: fix missed wakeup due to reordering of load

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Message-ID: <20170727165939.vomkrhpkyzvpxrbg@hirez.programming.kicks-ass.net>
Date:   Thu, 27 Jul 2017 18:59:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Prateek Sood <prsood@...eaurora.org>, mingo@...hat.com,
        sramana@...eaurora.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rwsem: fix missed wakeup due to reordering of load

On Thu, Jul 27, 2017 at 11:48:53AM -0400, Waiman Long wrote:
> atomic_long_sub_return_release() is implmented.

I've not had time to really thing about the problem at hand, but this I
can answer:

TSO (x86, s390, sparc): fully serialized
PPC: lwsync; ll/sc	(RCpc)
ARM64: ll/sc-release	(RCsc)
other: smp_mb(); atomic_sub_return_relaxed();