Re: [PATCH] HWPOISON: add a pr_err message when forcibly send a sigbus

[Shuai Xue]

On 2023/8/31 06:18, Will Deacon wrote:
> On Mon, Aug 28, 2023 at 09:41:55AM +0800, Shuai Xue wrote:
>> On 2023/8/22 09:15, Shuai Xue wrote:
>>> On 2023/8/21 18:50, Will Deacon wrote:
>>>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>>>> index 3fe516b32577..38e2186882bd 100644
>>>>> --- a/arch/arm64/mm/fault.c
>>>>> +++ b/arch/arm64/mm/fault.c
>>>>> @@ -679,6 +679,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>>>>>  	} else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) {
>>>>>  		unsigned int lsb;
>>>>>  
>>>>> +		pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
>>>>> +		       current->comm, current->pid, far);
>>>>>  		lsb = PAGE_SHIFT;
>>>>>  		if (fault & VM_FAULT_HWPOISON_LARGE)
>>>>>  			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
>>>>
>>>> Hmm, I'm not convinced by this. We have 'show_unhandled_signals' already,
>>>> and there's plenty of code in memory-failure.c for handling poisoned pages
>>>> reported by e.g. GHES. I don't think dumping extra messages in dmesg from
>>>> the arch code really adds anything.
>>>
>>> I see the show_unhandled_signals() will dump the stack but it rely on
>>> /proc/sys/debug/exception-trace be set.
>>>
>>> The memory failure is the top issue in our production cloud and also other hyperscalers.
>>> We have received complaints from our operations engineers and end users that processes
>>> are being inexplicably killed :(. Could you please consider add a message?
> 
> I don't have any objection to logging this stuff somehow, I'm just not
> convinced that the console is the best place for that information in 2023.
> Is there really nothing better?
> 

Hi, Will,

I agree that console might not the better place, but it still plays an important role.
IMO the most direct idea for end user to check what happened is to check by viewing
the dmesg. In addition, we deployed some log store service collects all cluster dmesg
from /var/log/kern.

Do you have any better choice?

+ @Tony for ERST
I found that after /dev/mcelog driver deprecated, both x86 and ARM64 platform does not
support to collect MCE record of previous boot in persistent storage via APEI ERST.
I propose to add a mechanism to do it for rasdaemon. Do you have any suggestion?

Thank you.
Best Regards,
Shuai