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Date:   Wed, 9 Dec 2020 18:22:04 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     John Ogness <john.ogness@linutronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@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
Message-ID: <20201209092204.GD1667627@google.com>
References: <20201201205341.3871-1-john.ogness@linutronix.de>
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On (20/12/09 09:16), Peter Zijlstra wrote:
> On Tue, Dec 08, 2020 at 11:36:44PM +0106, John Ogness wrote:
> > For the state variable we chose atomic_long_t instead of atomic64_t for
> > this reason. atomic_long_t operations are available atomically on all
> > architectures.
> 
> Please put on your eye cancer gear and inspect the atomic implementation
> of PA-RISC, Sparc32, feh, I forgot who else.
> 
> Those SMP capable architectures are gifted with just one XCHG like
> atomic instruction :/ Anyway, as said in the other email, they also
> don't have NMIs so it mostly works.

Hmm, wow. OK, I definitely want to look further.

When some CONFIG_DEBUG_FOO_BAR code wants to pr_err from prb->atomic_op
on those archs then we deadlock in printk once again?

	-ss