Re: [PATCH v2 01/12] uprobes: update outdated comment

Oleg Nesterov
2024-07-03T11:40:17Z

Sorry for the late reply. I'll try to read this version/discussion
when I have time... yes, I have already promised this before, sorry :/

On 07/01, Andrii Nakryiko wrote:
>
> There is no task_struct passed into get_user_pages_remote() anymore,
> drop the parts of comment mentioning NULL tsk, it's just confusing at
> this point.

Agreed.

> @@ -2030,10 +2030,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
> goto out;
>
> /*
> - * The NULL 'tsk' here ensures that any faults that occur here
> - * will not be accounted to the task. 'mm' *is* current->mm,
> - * but we treat this as a 'remote' access since it is
> - * essentially a kernel access to the memory.
> + * 'mm' *is* current->mm, but we treat this as a 'remote' access since
> + * it is essentially a kernel access to the memory.
> */
> result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL);

OK, this makes it less confusing, so

Acked-by: Oleg Nesterov <oleg@redhat.com>

---------------------------------------------------------------------
but it still looks confusing to me. This code used to pass tsk = NULL
only to avoid tsk->maj/min_flt++ in faultin_page().

But today mm_account_fault() increments these counters without checking
FAULT_FLAG_REMOTE, mm == current->mm, so it seems it would be better to
just use get_user_pages() and remove this comment?

Oleg.