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

[Jann Horn]

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

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