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Date:   Wed, 10 Jul 2019 14:32:38 -0700
Message-Id: <20190710213238.91835-1-henryburns@google.com>
Mime-Version: 1.0
Subject: [PATCH] mm/z3fold.c: remove z3fold_migration trylock
From:   Henry Burns <henryburns@google.com>
To:     Vitaly Wool <vitalywool@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Vitaly Vul <vitaly.vul@sony.com>,
        Shakeel Butt <shakeelb@google.com>,
        Jonathan Adams <jwadams@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Snild Dolkow <snild@sony.com>,
        Thomas Gleixner <tglx@linutronix.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Henry Burns <henryburns@google.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

z3fold_page_migrate() will never succeed because it attempts to acquire a
lock that has already been taken by migrate.c in __unmap_and_move().

__unmap_and_move() migrate.c
  trylock_page(oldpage)
  move_to_new_page(oldpage_newpage)
    a_ops->migrate_page(oldpage, newpage)
      z3fold_page_migrate(oldpage, newpage)
        trylock_page(oldpage)


Signed-off-by: Henry Burns <henryburns@google.com>
---
 mm/z3fold.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 985732c8b025..9fe9330ab8ae 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1335,16 +1335,11 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
 	zhdr = page_address(page);
 	pool = zhdr_to_pool(zhdr);
 
-	if (!trylock_page(page))
-		return -EAGAIN;
-
 	if (!z3fold_page_trylock(zhdr)) {
-		unlock_page(page);
 		return -EAGAIN;
 	}
 	if (zhdr->mapped_count != 0) {
 		z3fold_page_unlock(zhdr);
-		unlock_page(page);
 		return -EBUSY;
 	}
 	new_zhdr = page_address(newpage);
@@ -1376,7 +1371,6 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
 	queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
 
 	page_mapcount_reset(page);
-	unlock_page(page);
 	put_page(page);
 	return 0;
 }
-- 
2.22.0.410.gd8fdbe21b5-goog