linux-kernel - Re: [PATCH 0/2] Make printk_deferred() work properly before percpu setup is done

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Date:   Fri, 27 Mar 2020 04:05:43 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH 0/2] Make printk_deferred() work properly before percpu
 setup is done

On Fri, Mar 27, 2020 at 3:45 AM Sergey Senozhatsky
<sergey.senozhatsky.work@...il.com> wrote:
> 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/

Ah, thanks, I didn't think of searching the list archives for an
existing pending patch...