linux-kernel - [PATCH] mm: fix page leak at nfs

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Message-Id: <f4b3dc07dfa55bf7931de36b03aa9ef7e3ff0490.1391785222.git.aquini@redhat.com>
Date:	Fri,  7 Feb 2014 13:19:54 -0200
From:	Rafael Aquini <aquini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	trond.myklebust@...marydata.com, jstancek@...hat.com,
	jlayton@...hat.com, mgorman@...e.de, riel@...hat.com,
	linux-nfs@...r.kernel.org, akpm@...ux-foundation.org,
	linux-mm@...ck.org
Subject: [PATCH] mm: fix page leak at nfs_symlink()

Changes committed by "a0b8cab3 mm: remove lru parameter from
__pagevec_lru_add and remove parts of pagevec API" have introduced
a call to add_to_page_cache_lru() which causes a leak in nfs_symlink() 
as now the page gets an extra refcount that is not dropped.

Jan Stancek observed and reported the leak effect while running test8 from
Connectathon Testsuite. After several iterations over the test case,
which creates several symlinks on a NFS mountpoint, the test system was
quickly getting into an out-of-memory scenario.

This patch fixes the page leak by dropping that extra refcount 
add_to_page_cache_lru() is grabbing. 

Signed-off-by: Jan Stancek <jstancek@...hat.com>
Signed-off-by: Rafael Aquini <aquini@...hat.com>
---
 fs/nfs/dir.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index be38b57..4a48fe4 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1846,6 +1846,11 @@ int nfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
 							GFP_KERNEL)) {
 		SetPageUptodate(page);
 		unlock_page(page);
+		/*
+		 * add_to_page_cache_lru() grabs an extra page refcount.
+		 * Drop it here to avoid leaking this page later.
+		 */
+		page_cache_release(page);
 	} else
 		__free_page(page);

-- 
1.8.5.3

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