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

From: Petr Mladek <pmladek@suse.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: John Ogness <john.ogness@linutronix.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces
Date: Mon, 8 Nov 2021 09:34:06 +0100	[thread overview]
Message-ID: <YYjg/s6oSzZ26Uv+@alley> (raw)
In-Reply-To: <20211107045116.1754411-1-npiggin@gmail.com>

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@gmail.com>

Reviewed-by: Petr Mladek <pmladek@suse.com>

We should add also

     Cc: stable@vger.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.
IMHO, it makes sense to get this into 5.16-rc1 or rc2.

Thank you both a lot for nailing this down and for the fix.

Best Regards,
Petr