linux-kernel - Re: [PATCH v2 3/4] x86/split_lock: Handle #AC exception for split lock

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Date:   Fri, 29 Jun 2018 10:47:19 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Alan Cox <alan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 3/4] x86/split_lock: Handle #AC exception for split
 lock

On 06/29/2018 10:39 AM, Fenghua Yu wrote:
> On Fri, Jun 29, 2018 at 10:29:08AM -0700, Dave Hansen wrote:
>> On 06/29/2018 10:16 AM, Fenghua Yu wrote:
>>> On Fri, Jun 29, 2018 at 09:33:54AM -0700, Luck, Tony wrote:
>>>>>> +	WARN_ONCE(1, "A split lock issue is detected. Please FIX it\n");
>>>>> But, warning here is also not super useful.  Shouldn't we be dumping out
>>>>> the info in 'regs' instead of the current context?  We don't care about
>>>>> the state in the #AC handler, we care about 'regs'.
>>> But WARN dump not only the state in the #AC handler, but also dump the regs
>>> in the current context. And WARN dumps stack.
>> Oh, I forgot about the fancy stack following.  That might give us useful
>> output, although mixed with useless output about the #AC handler.
> The useful split lock info follows useless #AC handler info.

Can we do better than this?

Why don't I see the page fault stack in oopses that result in page
fault, for instance?