z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
However, zhdr contains fields that can't be directly coppied over (ex:
list_head, a circular linked list). We only need to initialize the
linked lists in new_zhdr, as z3fold_isolate_page() already ensures
that these lists are empty.
Additionally it is possible that zhdr->work has been placed in a
workqueue. In this case we shouldn't migrate the page, as zhdr->work
references zhdr as opposed to new_zhdr.
Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
Signed-off-by: Henry Burns <[email protected]>
---
mm/z3fold.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 42ef9955117c..9da471bcab93 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
z3fold_page_unlock(zhdr);
return -EBUSY;
}
+ if (work_pending(&zhdr->work)) {
+ z3fold_page_unlock(zhdr);
+ return -EAGAIN;
+ }
new_zhdr = page_address(newpage);
memcpy(new_zhdr, zhdr, PAGE_SIZE);
newpage->private = page->private;
page->private = 0;
z3fold_page_unlock(zhdr);
spin_lock_init(&new_zhdr->page_lock);
+ INIT_WORK(&new_zhdr->work, compact_page_work);
+ /*
+ * z3fold_page_isolate() ensures that this list is empty, so we only
+ * have to reinitialize it.
+ */
+ INIT_LIST_HEAD(&new_zhdr->buddy);
new_mapping = page_mapping(page);
__ClearPageMovable(page);
ClearPagePrivate(page);
--
2.22.0.510.g264f2c817a-goog
On Mon, Jul 15, 2019 at 9:47 AM Henry Burns <[email protected]> wrote:
>
> z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
> However, zhdr contains fields that can't be directly coppied over (ex:
> list_head, a circular linked list). We only need to initialize the
> linked lists in new_zhdr, as z3fold_isolate_page() already ensures
> that these lists are empty.
>
> Additionally it is possible that zhdr->work has been placed in a
> workqueue. In this case we shouldn't migrate the page, as zhdr->work
> references zhdr as opposed to new_zhdr.
>
> Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
> Signed-off-by: Henry Burns <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
> ---
> mm/z3fold.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 42ef9955117c..9da471bcab93 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
> z3fold_page_unlock(zhdr);
> return -EBUSY;
> }
> + if (work_pending(&zhdr->work)) {
> + z3fold_page_unlock(zhdr);
> + return -EAGAIN;
> + }
> new_zhdr = page_address(newpage);
> memcpy(new_zhdr, zhdr, PAGE_SIZE);
> newpage->private = page->private;
> page->private = 0;
> z3fold_page_unlock(zhdr);
> spin_lock_init(&new_zhdr->page_lock);
> + INIT_WORK(&new_zhdr->work, compact_page_work);
> + /*
> + * z3fold_page_isolate() ensures that this list is empty, so we only
> + * have to reinitialize it.
> + */
> + INIT_LIST_HEAD(&new_zhdr->buddy);
> new_mapping = page_mapping(page);
> __ClearPageMovable(page);
> ClearPagePrivate(page);
> --
> 2.22.0.510.g264f2c817a-goog
>
>>
>> z3fold_page_migration() calls memcpy(new_zhdr, zhdr, PAGE_SIZE).
>> However, zhdr contains fields that can't be directly coppied over (ex:
>> list_head, a circular linked list). We only need to initialize the
>> linked lists in new_zhdr, as z3fold_isolate_page() already ensures
>> that these lists are empty.
>>
>> Additionally it is possible that zhdr->work has been placed in a
>> workqueue. In this case we shouldn't migrate the page, as zhdr->work
>> references zhdr as opposed to new_zhdr.
>>
>> Fixes: bba4c5f96ce4 ("mm/z3fold.c: support page migration")
>> Signed-off-by: Henry Burns <[email protected]>
>> ---
>> mm/z3fold.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index 42ef9955117c..9da471bcab93 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -1352,12 +1352,22 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
>> z3fold_page_unlock(zhdr);
>> return -EBUSY;
>> }
>> + if (work_pending(&zhdr->work)) {
>> + z3fold_page_unlock(zhdr);
>> + return -EAGAIN;
>> + }
>> new_zhdr = page_address(newpage);
>> memcpy(new_zhdr, zhdr, PAGE_SIZE);
>> newpage->private = page->private;
>> page->private = 0;
>> z3fold_page_unlock(zhdr);
>> spin_lock_init(&new_zhdr->page_lock);
>> + INIT_WORK(&new_zhdr->work, compact_page_work);
>> + /*
>> + * z3fold_page_isolate() ensures that this list is empty, so we only
>> + * have to reinitialize it.
>> + */
>
>
> On the nitpicking side, we seem to have ensured that directly in migrate :) Looks OK to me otherwise.
Ok, I see it happens in the call to do_compact_page(). Got it, new
patch coming out now.
>
> ~Vitaly
>
>> + INIT_LIST_HEAD(&new_zhdr->buddy);
>> new_mapping = page_mapping(page);
>> __ClearPageMovable(page);
>> ClearPagePrivate(page);
>> --
>> 2.22.0.510.g264f2c817a-goog
>>
Sorry Vitaly, I had the wrong impression from your email that
INIT_LIST_HEAD() was being ensured directly in migrate and got
confused. (I thought you were saying it happened through the call to
do_compact_page() queued).
That being said, I don't see where in migrate new_zhdr->buddy is being
checked. We do check for new_zhdr.work with
if (work_pending(&zhdr->work)) {
...
}
Is that what you were referring to?