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

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Date:   Wed, 4 Sep 2019 08:38:36 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     sunqiuyang <sunqiuyang@...wei.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/1] mm/migrate: fix list corruption in migration of
 non-LRU movable pages

On Wed 04-09-19 02:18:38, sunqiuyang wrote:
> The isolate path of non-lru movable pages:
> 
> isolate_migratepages_block
> 	isolate_movable_page
> 		trylock_page
> 		// if PageIsolated, goto out_no_isolated
> 		a_ops->isolate_page
> 		__SetPageIsolated
> 		unlock_page
> 	list_add(&page->lru, &cc->migratepages)
> 
> The migration path:
> 
> unmap_and_move
> 	__unmap_and_move
> 		lock_page
> 		move_to_new_page
> 			a_ops->migratepage
> 			__ClearPageIsolated
> 		unlock_page
> 	/* here, the page could be isolated again by another thread, and added into another cc->migratepages,
> 	since PG_Isolated has been cleared, and not protected by page_lock */
> 	list_del(&page->lru)

But the page has been migrated already and not freed yet because there
is still a pin on it. So nobody should be touching it at this stage.
Or do I still miss something?
-- 
Michal Hocko
SUSE Labs