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Date: Tue, 15 May 2018 19:58:05 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Davidlohr Bueso <dave@stgolabs.net>,
        "Theodore Y. Ts'o" <tytso@mit.edu>, Oleg Nesterov <oleg@redhat.com>,
        Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.cz>,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership
 transfer by setting RWSEM_OWNER_UNKNOWN
Message-ID: <20180515175805.GN12217@hirez.programming.kicks-ass.net>
References: <1526405884-4860-1-git-send-email-longman@redhat.com>
 <1526405884-4860-3-git-send-email-longman@redhat.com>
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On Tue, May 15, 2018 at 01:38:04PM -0400, Waiman Long wrote:
> +/*
> + * Owner value to indicate the rwsem's owner is not currently known.
> + */
> +#define RWSEM_OWNER_UNKNOWN	((struct task_struct *)-1)

It might be nice to comment that this works and relies on having that
ANON_OWNER bit set.