Re: + uprobe-use-original-page-when-all-uprobes-are-removed.patch added to -mm tree

Re: + uprobe-use-original-page-when-all-uprobes-are-removed.patch added to -mm tree

[Oleg Nesterov]

I didn't see this version, so let me reply here.

On 07/26, Andrew Morton wrote:
>
> +	/* try orig_page only for unregister and anonymous old_page */
> +	if (!is_register && PageAnon(old_page)) {

Well, this is confusing... nothing really wrong, but we certainly do not
want to install the new anonymous page if !is_register && !PageAnon(old).
And in this case we do not even want to call __replace page().

OK, I won't insist, this should almost never happen, but again, please
see https://lore.kernel.org/lkml/20190726084423.GA16112@redhat.com/

> +		struct page *orig_page;
> +		pgoff_t index;
> +
> +		index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
> +		orig_page = find_get_page(vma->vm_file->f_inode->i_mapping,
> +					  index);
> +
> +		if (orig_page) {
> +			if (PageUptodate(orig_page) &&
> +			    pages_identical(new_page, orig_page)) {
> +				/* let go new_page */
> +				put_page(new_page);
> +				new_page = NULL;
> +
> +				/* dec_mm_counter for old_page */
> +				dec_mm_counter(mm, MM_ANONPAGES);

this assumes that __replace_page() can't fail, but it can. I think you
should move this into into __replace_page().

Oleg.

Re: + uprobe-use-original-page-when-all-uprobes-are-removed.patch added to -mm tree

[Song Liu]

> On Jul 29, 2019, at 8:05 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> 
> I didn't see this version, so let me reply here.
> 
> On 07/26, Andrew Morton wrote:
>> 
>> +	/* try orig_page only for unregister and anonymous old_page */
>> +	if (!is_register && PageAnon(old_page)) {
> 
> Well, this is confusing... nothing really wrong, but we certainly do not
> want to install the new anonymous page if !is_register && !PageAnon(old).
> And in this case we do not even want to call __replace page().
> 
> OK, I won't insist, this should almost never happen, but again, please
> see https://lore.kernel.org/lkml/20190726084423.GA16112@redhat.com/

I see. Do you want me fold this patch with 2/4? 

> 
>> +		struct page *orig_page;
>> +		pgoff_t index;
>> +
>> +		index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
>> +		orig_page = find_get_page(vma->vm_file->f_inode->i_mapping,
>> +					  index);
>> +
>> +		if (orig_page) {
>> +			if (PageUptodate(orig_page) &&
>> +			    pages_identical(new_page, orig_page)) {
>> +				/* let go new_page */
>> +				put_page(new_page);
>> +				new_page = NULL;
>> +
>> +				/* dec_mm_counter for old_page */
>> +				dec_mm_counter(mm, MM_ANONPAGES);
> 
> this assumes that __replace_page() can't fail, but it can. I think you
> should move this into into __replace_page().

Good catch! Let me fix it. 

Hi Andrew,

Do you prefer a whole v10 (1/4 to 4/4) or just newer version of this 
one (2/4)?

Thanks,
Song 

Re: + uprobe-use-original-page-when-all-uprobes-are-removed.patch added to -mm tree

[Andrew Morton]

On Mon, 29 Jul 2019 17:04:05 +0000 Song Liu <songliubraving@fb.com> wrote:

> > this assumes that __replace_page() can't fail, but it can. I think you
> > should move this into into __replace_page().
> 
> Good catch! Let me fix it. 
> 
> Hi Andrew,
> 
> Do you prefer a whole v10 (1/4 to 4/4) or just newer version of this 
> one (2/4)?

Either is OK.  I guess just a new 2/4 is sufficient, if the difference
is minor.

Re: + uprobe-use-original-page-when-all-uprobes-are-removed.patch added to -mm tree

[Song Liu]

> On Jul 30, 2019, at 12:17 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> On Mon, 29 Jul 2019 17:04:05 +0000 Song Liu <songliubraving@fb.com> wrote:
> 
>>> this assumes that __replace_page() can't fail, but it can. I think you
>>> should move this into into __replace_page().
>> 
>> Good catch! Let me fix it. 
>> 
>> Hi Andrew,
>> 
>> Do you prefer a whole v10 (1/4 to 4/4) or just newer version of this 
>> one (2/4)?
> 
> Either is OK.  I guess just a new 2/4 is sufficient, if the difference
> is minor.

I sent v10 last night. Then Oleg found some issue with 3/4 (thanks!) Let
me resend 2/4 (with change in commit log) and 3/4 (with code change). 

Thanks,
Song