Re: [PATCH] ACPI: APEI: do not add task_work for outside context error

[Shuai Xue <xueshuai@linux.alibaba.com>]

在 2022/9/16 PM1:05, Shuai Xue 写道:
> If an error is detected as a result of user-space process accessing a
> corrupt memory location, the CPU may take an abort. Then the platform
> firmware reports kernel via NMI like notifications, e.g. NOTIFY_SEA,
> NOTIFY_SOFTWARE_DELEGATED, etc.
> 
> For NMI like notifications, commit 7f17b4a121d0 ("ACPI: APEI: Kick the
> memory_failure() queue for synchronous errors") keep track of whether
> memory_failure() work was queued, and make task_work pending to flush out
> the queue so that the work is processed before return to user-space.
> 
> The code use init_mm to check whether the error occurs in user space:
> 
>     if (current->mm != &init_mm)
> 
> The condition is always true, becase _nobody_ ever has "init_mm" as a real
> VM any more 

(Sorry, I forgot to describe the side effect.)

If an error is detected outside of the current execution context (e.g. when
detected by a background scrubber), the current could be any thread. When a
kernel thread is interrupted, the work ghes_kick_task_work deferred to task_work
will never be processed because entry_handler returns to call ret_to_kernel()
instead of ret_to_user(). Consequently, the estatus_node alloced from
ghes_estatus_pool in ghes_in_nmi_queue_one_entry will not be released. After
around 200 allocations in our platform, the ghes_estatus_pool will run of memory
and ghes_in_nmi_queue_one_entry returns ENOMEM. As a result, the event failed
to be processed.

    sdei: event 805 on CPU 113 failed with error: -2

Finally, a lot of unhandled events may cause platform firmware to exceed some
threshold and reboot.

Best Regards,
Shuai

and should generally just do
> 
>     if (current->mm)
> 
> as described in active_mm.rst documentation.
> 
> Then if an error is detected outside of the current execution context (e.g.
> when detected by a background scrubber), do not add task_work as the
> original patch intends to do.
> 
> Fixes: 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for synchronous errors")
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> ---
>  drivers/acpi/apei/ghes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index d91ad378c00d..80ad530583c9 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -985,7 +985,7 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
>  				ghes_estatus_cache_add(generic, estatus);
>  		}
>  
> -		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,