linux-kernel - Re: [PATCH v2 00/17] [request for stable 3.10 inclusion] x86/nmi: Print all cpu stacks from NMI safely

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Date:	Tue, 19 May 2015 14:57:46 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Wang Long <long.wanglong@...wei.com>
Cc:	rostedt@...dmis.org, jkosina@...e.cz, gregkh@...uxfoundation.org,
	stable@...r.kernel.org, peifeiyue@...wei.com,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	dzickus@...hat.com, x86@...nel.org, morgan.wang@...wei.com,
	sasha.levin@...cle.com
Subject: Re: [PATCH v2 00/17] [request for stable 3.10 inclusion] x86/nmi:
 Print all cpu stacks from NMI safely

On Tue 2015-05-19 09:08:45, Wang Long wrote:
> This is my backport patch series to Fix the problem(backport to 3.10):
> "
> When trigger_all_cpu_backtrace() is called on x86, it will trigger an
> NMI on each CPU and call show_regs(). But this can lead to a hard lock
> up if the NMI comes in on another printk().
> "
> The solution is described in commit "a9edc88093287183ac934be44f295f183b2c62dd":
> when the NMI triggers, it switches the printk routine for that CPU to call 
> a NMI safe printk function that records the printk in a per_cpu seq_buf 
> descriptor. After all NMIs have finished recording its data, the trace_
> seqs are printed in a safe context.
> 
> The solution use "switch printk routine" and "seq_buf" infrastructures, but the
> 3.10 stable have no both of them.
> 
> The patch 1-13 backport the "seq_buf" infrastructures. in detail, patch 1, 2
> and 6 only backport "seq_buf" related code.
> 
> The patch 14-15 backport the "switch printk routine".
> 
> The patch 16-17 is the patch to print all cpu stacks from NMI safely
> 
> as discussed in https://lkml.org/lkml/2015/5/13/497, in 3.10 stable, this is 
> the only way to solve the problem and the backport code is a bit more.
> 
> v1 -> v2:
>  * fix the indent error.
>  * rebase on 3.10.79
> 
> Any thoughts?

Please, wait with the integration. I am testing it with a storm of
sysrq requests:

    $> while true ; do echo l >/proc/sysrq-trigger ; done

with iptables enabled:

    $> iptables -A INPUT -j LOG --log-prefix "incomming packet:"

and storm of pings from other machine:

    $> ping -f <patched-host>


The machine somehow freezes. It does not make sense. I am trying to investigate.

Best Regards,
Petr
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