linux-kernel - Re: [PATCH] printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces

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Date:   Mon, 08 Nov 2021 23:43:31 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printk: restore flushing of NMI buffers on remote CPUs
 after NMI backtraces

Excerpts from Petr Mladek's message of November 8, 2021 6:34 pm:
> On Sun 2021-11-07 14:51:16, Nicholas Piggin wrote:
>> printk from NMI context relies on irq work being raised on the local CPU
>> to print to console. This can be a problem if the NMI was raised by a
>> lockup detector to print lockup stack and regs, because the CPU may not
>> enable irqs (because it is locked up).
>> 
>> Introduce printk_trigger_flush() that can be called another CPU to try
>> to get those messages to the console, call that where printk_safe_flush
>> was previously called.
>> 
>> Fixes: 93d102f094be ("printk: remove safe buffers")
>> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> 
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> 
> We should add also
> 
>      Cc: stable@...r.kernel.org # 5.15
> 
> No need to resent the patch. I could add it when pushing.
> 
> Plan: I am going to wait one or more days for a potential feedback
> and ack from John. Then I am going to push this into printk/linux.git.

That sounds good to me.

> IMHO, it makes sense to get this into 5.16-rc1 or rc2.

Agree.

Thanks,
Nick

> Thank you both a lot for nailing this down and for the fix.
> 
> Best Regards,
> Petr
>