linux-kernel - Re: [PATCH -next v2] locking/osq_lock: annotate a data race in osq

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Message-Id: <D9C5B7E9-5927-4015-BC7C-202585C5649E@lca.pw>
Date:   Mon, 11 May 2020 13:10:27 -0400
From:   Qian Cai <cai@....pw>
To:     Will Deacon <will@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Elver Marco <elver@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH -next v2] locking/osq_lock: annotate a data race in osq_lock



> On May 11, 2020, at 12:54 PM, Will Deacon <will@...nel.org> wrote:
> 
> Hmm, I don't see how it can remove the cmpxchg(). Do you have a link to that
> discussion, please?

lore.kernel.org/lkml/20200211124753.GP14914@...ez.programming.kicks-ass.net

Correction — if compilers could prove ”prev->next != node” is always true, that cmpxchg() would not run. cpu_relax() should be sufficient to keep that “if statement” been optimized away in any case.