linux-kernel - [PATCH v3] mm/z3fold.c: Lock z3fold page before _

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Date:   Tue,  2 Jul 2019 16:35:38 -0700
From:   Henry Burns <henryburns@...gle.com>
To:     Vitaly Wool <vitalywool@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vitaly Vul <vitaly.vul@...y.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Xidong Wang <wangxidong_97@....com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jonathan Adams <jwadams@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Henry Burns <henryburns@...gle.com>,
        David Rientjes <rientjes@...gle.com>, stable@...r.kernel.org
Subject: [PATCH v3] mm/z3fold.c: Lock z3fold page before  __SetPageMovable()

Following zsmalloc.c's example we call trylock_page() and unlock_page(). 
Also make z3fold_page_migrate() assert that newpage is passed in locked,
as per the documentation.

Link: http://lkml.kernel.org/r/20190702005122.41036-1-henryburns@google.com
Signed-off-by: Henry Burns <henryburns@...gle.com>
Suggested-by: Vitaly Wool <vitalywool@...il.com>
Acked-by: Vitaly Wool <vitalywool@...il.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Shakeel Butt <shakeelb@...gle.com>
Cc: Vitaly Vul <vitaly.vul@...y.com>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Xidong Wang <wangxidong_97@....com>
Cc: Jonathan Adams <jwadams@...gle.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
 Changelog since v2:
 - Removed the WARN_ON entirely, as it is an expected code path.

 Changelog since v1:
 - Added an if statement around WARN_ON(trylock_page(page)) to avoid
   unlocking a page locked by a someone else.

 mm/z3fold.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index e174d1549734..eeb3fe7f5ca3 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -918,7 +918,16 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 		set_bit(PAGE_HEADLESS, &page->private);
 		goto headless;
 	}
-	__SetPageMovable(page, pool->inode->i_mapping);
+	if (can_sleep) {
+		lock_page(page);
+		__SetPageMovable(page, pool->inode->i_mapping);
+		unlock_page(page);
+	} else {
+		if (!trylock_page(page)) {
+			__SetPageMovable(page, pool->inode->i_mapping);
+			unlock_page(page);
+		}
+	}
 	z3fold_page_lock(zhdr);
 
 found:
@@ -1325,6 +1334,7 @@ static int z3fold_page_migrate(struct address_space *mapping, struct page *newpa
 
 	VM_BUG_ON_PAGE(!PageMovable(page), page);
 	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
 	zhdr = page_address(page);
 	pool = zhdr_to_pool(zhdr);
-- 
2.22.0.410.gd8fdbe21b5-goog