linux-kernel - [PATCH v2] mm/z3fold.c: Reinitialize zhdr structs after migration

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Message-Id: <20190716000520.230595-1-henryburns@google.com>
Date:   Mon, 15 Jul 2019 17:05:20 -0700
From:   Henry Burns <henryburns@...gle.com>
To:     Vitaly Vul <vitaly.vul@...y.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jonathan Adams <jwadams@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Henry Burns <henryburns@...gle.com>
Subject: [PATCH v2] mm/z3fold.c: Reinitialize zhdr structs after migration

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 <henryburns@...gle.com>
---
 Changelog since v1:
 - Made comments explicityly refer to new_zhdr->buddy.

 mm/z3fold.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 42ef9955117c..f4b2283b19a3 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 new_zhdr->buddy 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