RE: [PATCH 1/1] mm/migrate: fix list corruption in migration of non-LRU movable pages

[sunqiuyang]

________________________________________
From: Michal Hocko [mhocko@xxxxxxxxxx]
Sent: Wednesday, September 04, 2019 16:14
To: sunqiuyang
Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx
Subject: Re: [PATCH 1/1] mm/migrate: fix list corruption in migration of non-LRU movable pages

Do not top post please

On Wed 04-09-19 07:27:25, sunqiuyang wrote:
> isolate_migratepages_block() from another thread may try to isolate the page again:
>
> for (; low_pfn < end_pfn; low_pfn++) {
>   /* ... */
>   page = pfn_to_page(low_pfn);
>  /* ... */
>   if (!PageLRU(page)) {
>     if (unlikely(__PageMovable(page)) && !PageIsolated(page)) {
>         /* ... */
>         if (!isolate_movable_page(page, isolate_mode))
>           goto isolate_success;
>       /*... */
> isolate_success:
>      list_add(&page->lru, &cc->migratepages);
>
> And this page will be added to another list.
> Or, do you see any reason that the page cannot go through this path?

The page shouldn't be __PageMovable after the migration is done. All the
state should have been transfered to the new page IIUC.

----
I don't see where page->mapping is modified after the migration is done. 

Actually, the last comment in move_to_new_page() says,
"Anonymous and movable page->mapping will be cleard by
free_pages_prepare so don't reset it here for keeping
the type to work PageAnon, for example. "

Or did I miss something? Thanks,

--
Michal Hocko
SUSE Labs