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Date:   Fri, 12 Mar 2021 13:26:47 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     paulmck@kernel.org
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
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        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 1/3] rcu: Provide polling interfaces for
 Tree RCU grace periods
Message-ID: <20210312122647.GC3646@lothringen>
References: <20210304002605.GA23785@paulmck-ThinkPad-P72>
 <20210304002632.23870-1-paulmck@kernel.org>
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On Wed, Mar 03, 2021 at 04:26:30PM -0800, paulmck@kernel.org wrote:
>  /**
> + * start_poll_state_synchronize_rcu - Snapshot and start RCU grace period
> + *
> + * Returns a cookie that is used by a later call to cond_synchronize_rcu()
> + * or poll_state_synchronize_rcu() to determine whether or not a full
> + * grace period has elapsed in the meantime.  If the needed grace period
> + * is not already slated to start, notifies RCU core of the need for that
> + * grace period.
> + *
> + * Interrupts must be enabled for the case where it is necessary to awaken
> + * the grace-period kthread.
> + */
> +unsigned long start_poll_synchronize_rcu(void)
> +{
> +	unsigned long flags;
> +	unsigned long gp_seq = get_state_synchronize_rcu();

Ah! It's using rcu_seq_snap() and not rcu_seq_current() and therefore it's
waiting for a safe future grace period, right?

If so, please discard my previous email.

Thanks.