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Date:   Mon, 7 Dec 2020 13:56:05 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t
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On Mon, Dec 07, 2020 at 11:09:39AM +0106, John Ogness wrote:
> That will not work. We are talking about a situation where the writer is
> preempted. So seq will never equal seq_copy in that situation. I expect
> that the seqcount_latch is necessary.

Interrupted rather, I would think, specifically NMIs? Then yes, latch
should work. Gets you either the old or new, but never something in
between.