[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <55548503.2050406@huawei.com>
Date: Thu, 14 May 2015 19:20:35 +0800
From: "long.wanglong" <long.wanglong@...wei.com>
To: Jiri Kosina <jkosina@...e.cz>
CC: 王龙 <wanglong@...qinren.net>,
rostedt <rostedt@...dmis.org>,
paulmck <paulmck@...ux.vnet.ibm.com>, pmladek <pmladek@...e.cz>,
dzickus <dzickus@...hat.com>,
johannes <johannes@...solutions.net>, koct9i <koct9i@...il.com>,
tglx <tglx@...utronix.de>, mingo <mingo@...hat.com>,
hpa <hpa@...or.com>, x86 <x86@...nel.org>,
atomlin <atomlin@...hat.com>, akpm <akpm@...ux-foundation.org>,
"sasha.levin" <sasha.levin@...cle.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
peifeiyue <peifeiyue@...wei.com>,
"morgan.wang" <morgan.wang@...wei.com>
Subject: Re: [RFC] how to perform a safe NMI stack trace on all CPUs on x86?
On 2015/5/13 22:26, Jiri Kosina wrote:
> On Wed, 13 May 2015, 王龙 wrote:
>
>> Hi all,
>>
>> In kernel before 3.19, 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 commit a9edc88093287183ac934be44f295f183b2c62dd (x86/nmi: Perform a safe
>> NMI stack trace on all CPUs) fix this problem on kernel mainline. 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 seq_bufs are printed in a safe
>> context. But how do we fix this problem in older version of kernel(eg, 3.10 stable)?
>> The 3.10 stable has no "switch printk routine" and "seq_buf" infrastructures.
>>
>> Could anyone give me some ideas?
>
> Either you backport seq_buf-based aproach to the older kernel, or, if you
> are working on 3.4 kernel or earlier (basically any kernel preceeding the
> printk() revamp that happened in 7ff9554bb57 and after), you can use
> slightly simpler aproach.
>
> It's an aproach we used initially when finding out the issue for the first
> time, and it is proven to work as well (but it's not applicable after Kay
> added all the complexity to printk()).
>
> You can see it in our SLE11 kernel tree, available on
>
> http://kernel.suse.com/cgit/kernel/commit/?h=SLE11-SP4&id=8d62ae68ff61d77ae3c4899f05dbd9c9742b14c9
>
> for example.
>
> It's up to you to judget which is the least painful way :)
>
Hi Jiri Kosina,
For 3.10 stable, the only way to solve this problem is backport seq_buf-based aproach.
I will backport necessary patches to 3.10 stable. Welcome you to review my backport patches.
Best Regards
Wang Long
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists