On Fri, Oct 21, 2022 at 09:52:01AM +0800, Shuai Xue wrote:

在 2022/10/21 AM4:05, Tony Luck 写道:

quoted

On Thu, Oct 20, 2022 at 09:57:04AM +0800, Shuai Xue wrote:

quoted

在 2022/10/20 AM1:08, Tony Luck 写道:

quoted

I'm experimenting with using sched_work() to handle the call to
memory_failure() (echoing what the machine check handler does using
task_work)_add() to avoid the same problem of not being able to directly
call memory_failure()).

Work queues permit work to be deferred outside of the interrupt context
into the kernel process context. If we return to user-space before the
queued memory_failure() work is processed, we will take the fault again,
as we discussed recently.

    commit 7f17b4a121d0d ACPI: APEI: Kick the memory_failure() queue for synchronous errors
    commit 415fed694fe11 ACPI: APEI: do not add task_work to kernel thread to avoid memory leak

So, in my opinion, we should add memory failure as a task work, like
do_machine_check does, e.g.

    queue_task_work(&m, msg, kill_me_maybe);

Maybe ... but this case isn't pending back to a user instruction
that is trying to READ the poison memory address. The task is just
trying to WRITE to any address within the page.

So this is much more like a patrol scrub error found asynchronously
by the memory controller (in this case found asynchronously by the
Linux page copy function).  So I don't feel that it's really the
responsibility of the current task.

When we do return to user mode the task is going to be busy servicing
a SIGBUS ... so shouldn't try to touch the poison page before the
memory_failure() called by the worker thread cleans things up.

quoted

+	INIT_WORK(&p->work, do_sched_memory_failure);
+	p->pfn = pfn;
+	schedule_work(&p->work);
+}

I think there is already a function to do such work in mm/memory-failure.c.

	void memory_failure_queue(unsigned long pfn, int flags)

Also pointed out by Miaohe Lin [off-list ref] ... this does
exacly what I want, and is working well in tests so far. So perhaps
a cleaner solution than making the kill_me_maybe() function globally
visible.

-Tony