Re: [PATCH v2] ACPI: APEI: do not add task_work to kernel thread to avoid memory leak

[Shuai Xue]

Hi, Tony,

在 2022/9/27 AM11:50, Shuai Xue 写道:
> 
> 
> 在 2022/9/26 PM11:20, Luck, Tony 写道:
>>>>
>>>> -               if (task_work_pending && current->mm != &init_mm) {
>>>> +               if (task_work_pending && current->mm) {
>>>>                         estatus_node->task_work.func = ghes_kick_task_work;
>>>>                         estatus_node->task_work_cpu = smp_processor_id();
>>>>                         ret = task_work_add(current, &estatus_node->task_work,
>>
>> It seems that you are getting errors reported while running kernel threads. This fix avoids
>> pointlessly adding "task_work" that will never be processed because kernel threads never
>> return to user mode.
> 
> Yes, you are right.
> 
>>
>> But maybe something else needs to be done? The code was, and with this fix still is,
>> taking no action for the error. That doesn't seem right.
> 
> Sorry, I don't think so. As far as I know, on Arm platform, hardware error can signal
> exceptions including:
> 
> - Synchronous External Abort (SEA), e,g. data abort or instruction abort
> - Asynchronous External Abort (signalled as SErrors), e,g. L2 can generate SError for
>   error responses from the interconnect for a Device or Non-cacheable store
> - Fault Handling and Error Recovery interrupts: DDR mainline/demand/scrubber error interrupt
> 
> When the error signals asynchronous exceptions (SError or interrupt), any kind of thread can
> be interrupted, including kernel thread. Because asynchronous exceptions are signaled in
> background, the errors are detected outside of the current execution context.
> 
> The GHES driver always queues work to handle memory failure of a page in memory_failure_queue().
> If a kernel thread is interrupted:
> 
> - Without this fix, the added task_work will never be processed so that the work will not
>   be canceled.
> - With this fix, the task_work will not be added.
> 
> In a conclusion, the error will be handled in a kworker with or without this fix.
> 
> The point of fix is that:
> 
> - The condition is useless because it is always tree. And I think it is not the original patch
>   intends to do.
> - The current code leads to memory leaks. The estatus_node will not be freed when task_work is
>   added to a kernel thread.
> 
> 
>>
>> Are you injecting errors to create this scenario? 
> 
> Yes, I am injecting error to create such scenario. After 200 injections, the ghes_estatus_pool
> will run of memory and ghes_in_nmi_queue_one_entry() returns ENOMEM. Finally, a lot of unhandled
> events may cause platform firmware to exceed some threshold and reboot.
> 
>> What does your test do?
> 
> My injection includes two steps:
> 
> - mmap a device memory for userspace in a driver
> - inject uc and trigger write like ras-tools does
> 
> I have opened source the code and you can find here[1]. It's forked from your repo and mainly based
> on your code :)
> 
> By the way, do you have any plans to extend ras-tools to Arm platform. And is there a mail-list
> for ras-tools? I send a mail to add test cases to ras-tools several weeks ago, but no response.
> May your mailbox regards it as Spam.
> 

Thank you for your review, but I am still having problems with this question.

Do you have any interest to extend ras-tools to Arm platform? I forked a arm-devel branch[1]
from your repo:

- port X86 arch specific cases to Arm platform
- add some common cases like hugetlb, thread and Arm specific cases like prefetch, strb, etc, which
  are helpful to test hardware and firmware RAS problems we encountered.

I am pleasure to contribute these code to your upstream repo and looking forward to see a more
powerful and cross platform tools to inject and debug RAS ability on both X86 and Arm platform.

I really appreciate your great work, and look forward to your reply. Thank you.

Best Regards,
Shuai

> [1] https://gitee.com/anolis/ras-tools/tree/arm-devel