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

[Sergey Senozhatsky]

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/

	-ss