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

["Jarkko Sakkinen" <jarkko@kernel.org>]

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@huawei.com>
> > >> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> > >>
> > >> ---
> > >>   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