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Date:   Fri, 27 Mar 2020 11:45:00 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Jann Horn <jannh@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        linux-kernel@vger.kernel.org, Dennis Zhou <dennis@kernel.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH 0/2] Make printk_deferred() work properly before percpu
 setup is done
Message-ID: <20200327024500.GA211096@google.com>
References: <20200326163245.119670-1-jannh@google.com>
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On (20/03/26 17:32), Jann Horn wrote:
> While I was doing some development work, I noticed that if you call
> printk_deferred() before percpu setup has finished, stuff breaks, and
> e.g. "dmesg -w" fails to print new messages.
> 
> This happens because writing to percpu memory before percpu
> initialization is done causes the modified percpu memory to be
> propagated from the boot CPU to all the secondary CPUs; and both the
> printk code as well as the irq_work implementation use percpu memory.
> 
> I think that printk_deferred() ought to work even before percpu
> initialization, since it is used by things like pr_warn_ratelimited()
> and the unwinder infrastructure. I'm not entirely sure though whether
> this is the best way to implement that, or whether it would be better to
> let printk_deferred() do something different if it is called during
> early boot.

Hi Jann,

I believe we have a patch for this issue

https://lore.kernel.org/lkml/20200303113002.63089-1-sergey.senozhatsky@gmail.com/

	-ss