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Date:   Fri, 15 May 2020 21:27:05 -0700
From:   Michel Lespinasse <walken@google.com>
To:     Lai Jiangshan <laijs@linux.alibaba.com>
Cc:     linux-kernel@vger.kernel.org,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Rik van Riel <riel@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH V2 2/2] rbtree_latch: don't need to check seq when it
 found a node
Message-ID: <20200516042705.GA82414@google.com>
References: <20200515150122.GY2957@hirez.programming.kicks-ass.net>
 <20200515155912.1713-1-laijs@linux.alibaba.com>
 <20200515155912.1713-2-laijs@linux.alibaba.com>
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On Fri, May 15, 2020 at 03:59:09PM +0000, Lai Jiangshan wrote:
> latch_tree_find() should be protected by caller via RCU or so.
> When it find a node in an attempt, the node must be a valid one
> in RCU's point's of view even the tree is (being) updated with a
> new node with the same key which is entirely subject to timing
> anyway.

I'm not sure I buy this. Even if we get a valid node, is it the one we
were searching for ? I don't see how this could be guaranteed if the
read raced with a tree rebalancing.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.