Re: [PATCH v12 1/3] ACPI: APEI: send SIGBUS to current task if synchronous memory error not recovered

[Jarkko Sakkinen]

On Fri Sep 6, 2024 at 4:53 AM EEST, Shuai Xue wrote:
>
>
> 在 2024/9/5 22:17, Jarkko Sakkinen 写道:
> > On Thu Sep 5, 2024 at 5:14 PM EEST, Jarkko Sakkinen wrote:
> >> On Thu Sep 5, 2024 at 6:04 AM EEST, Shuai Xue wrote:
> >>>
> >>>
> >>> 在 2024/9/4 00:09, Jarkko Sakkinen 写道:
> >>>> On Mon Sep 2, 2024 at 6:00 AM EEST, Shuai Xue wrote:
> >>>>> Synchronous error was detected as a result of user-space process accessing
> >>>>> a 2-bit uncorrected error. The CPU will take a synchronous error exception
> >>>>> such as Synchronous External Abort (SEA) on Arm64. The kernel will queue a
> >>>>> memory_failure() work which poisons the related page, unmaps the page, and
> >>>>> then sends a SIGBUS to the process, so that a system wide panic can be
> >>>>> avoided.
> >>>>>
> >>>>> However, no memory_failure() work will be queued unless all bellow
> >>>>> preconditions check passed:
> >>>>>
> >>>>> - `if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))` in ghes_handle_memory_failure()
> >>>>> - `if (flags == -1)` in ghes_handle_memory_failure()
> >>>>> - `if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))` in ghes_do_memory_failure()
> >>>>> - `if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) ` in ghes_do_memory_failure()
> >>>>>
> >>>>> In such case, the user-space process will trigger SEA again.  This loop
> >>>>> can potentially exceed the platform firmware threshold or even trigger a
> >>>>> kernel hard lockup, leading to a system reboot.
> >>>>>
> >>>>> Fix it by performing a force kill if no memory_failure() work is queued
> >>>>> for synchronous errors.
> >>>>>
> >>>>> Suggested-by: Xiaofei Tan <tanxiaofei@xxxxxxxxxx>
> >>>>> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
> >>>>>
> >>>>> ---
> >>>>>    drivers/acpi/apei/ghes.c | 10 ++++++++++
> >>>>>    1 file changed, 10 insertions(+)
> >>>>>
> >>>>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> >>>>> index 623cc0cb4a65..b0b20ee533d9 100644
> >>>>> --- a/drivers/acpi/apei/ghes.c
> >>>>> +++ b/drivers/acpi/apei/ghes.c
> >>>>> @@ -801,6 +801,16 @@ static bool ghes_do_proc(struct ghes *ghes,
> >>>>>    		}
> >>>>>    	}
> >>>>>    
> >>>>> +	/*
> >>>>> +	 * If no memory failure work is queued for abnormal synchronous
> >>>>> +	 * errors, do a force kill.
> >>>>> +	 */
> >>>>> +	if (sync && !queued) {
> >>>>> +		pr_err("Sending SIGBUS to %s:%d due to hardware memory corruption\n",
> >>>>> +			current->comm, task_pid_nr(current));
> >>>>
> >>>> Hmm... doest this need "hardware" or would "memory corruption" be
> >>>> enough?
> >>>>
> >>>> Also, does this need to say that it is sending SIGBUS when the signal
> >>>> itself tells that already?
> >>>>
> >>>> I.e. could "%s:%d has memory corruption" be enough information?
> >>>
> >>> Hi, Jarkko,
> >>>
> >>> Thank you for your suggestion. Maybe it could.
> >>>
> >>> There are some similar error info which use "hardware memory error", e.g.
> >>
> >> By tweaking my original suggestion just a bit:
> >>
> >> "%s:%d: hardware memory corruption"
> >>
> >> Can't get clearer than that, right?
> > 
> > And obvious reason that shorter and more consistent klog message is easy
> > to spot and grep. It is simply less convoluted.
> > 
> > If you want also SIGBUS, I'd just put it as "%s:%d: hardware memory
> > corruption (SIGBUS)"
> > 
> > BR, Jarkko
>
> Hi, Jarkko,
>
> I will change it to "%s:%d: hardware memory corruption (SIGBUS)".
>
> Thank you for valuable suggestion.

Yeah, no intention nitpick, it has a practical value when debugging
issues :-)

>
> Best Regards,
> Shuai

BR, Jarkko