linux-ext4 - [PATCH] fs: take i_mutex in __page

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Date:	Mon,  1 Apr 2013 11:23:42 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>
Subject: [PATCH] fs: take i_mutex in __page_symlink()

In Documentation/filesystems/Locking, it's documented that
write_begin() is guaranteed to be called with i_mutex locked.  The
function __page_symlink() was not taking i_mutex before calling
pagecache_write_begin(), which will eventually result in the file
system's write_begin()'s function getting called.

Other callers of pagecache_write_begin such as in fs/splice.c, call
pagecache_write_begin() with i_mutex locked, so fix __page_symlink()
to be consistent.

This was discovered by the addition of a new ext4 debugging assertion
which checked to make sure i_mutex was locked before calling
ext4_truncate().

Reported-by: Zheng Liu <gnehzuil.liu@...il.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Cc: linux-fsdevel@...r.kernel.org
Cc: Al Viro <viro@...IV.linux.org.uk>
---

Note: I plan to carry the following patch in the ext4 tree, unless
someone objects or Al insists on carrying this in the vfs git tree.

 fs/namei.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 57ae9c8..548e57b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4035,8 +4035,10 @@ int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
 		flags |= AOP_FLAG_NOFS;

 retry:
+	mutex_lock(&inode->i_mutex);
 	err = pagecache_write_begin(NULL, mapping, 0, len-1,
 				flags, &page, &fsdata);
+	mutex_unlock(&inode->i_mutex);
 	if (err)
 		goto fail;

-- 
1.7.12.rc0.22.gcdd159b

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