linux-kernel - mnt_want_write_file() has problem?

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Message-ID: <871vnt7vac.fsf@devron.myhome.or.jp>
Date:	Mon, 03 Aug 2009 06:36:27 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Al Viro <viro@...iv.linux.org.uk>, Nick Piggin <npiggin@...e.de>
Cc:	linux-kernel@...r.kernel.org
Subject: mnt_want_write_file() has problem?

Hi,

While I'm reading some code, I suspected that mnt_want_write_file() may
have wrong assumption.  I think mnt_want_write_file() is assuming it
increments ->mnt_writers if (file->f_mode & FMODE_WRITE). But, if it's
special_file(), it is false?

Sorry, I'm still not checking all of those though. E.g. I'm thinking the
below.

static inline int __get_file_write_access(struct inode *inode,
					  struct vfsmount *mnt)
{
[...]
	if (!special_file(inode->i_mode)) {
		/*
		 * Balanced in __fput()
		 */
		error = mnt_want_write(mnt);
		if (error)
			put_write_access(inode);
	}
	return error;
}

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>

Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
---

 fs/namespace.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN fs/namespace.c~mnt_want_write-wrong-assume fs/namespace.c
--- linux-2.6/fs/namespace.c~mnt_want_write-wrong-assume	2009-08-03 04:33:35.000000000 +0900
+++ linux-2.6-hirofumi/fs/namespace.c	2009-08-03 04:31:34.000000000 +0900
@@ -316,7 +316,8 @@ EXPORT_SYMBOL_GPL(mnt_clone_write);
  */
 int mnt_want_write_file(struct file *file)
 {
-	if (!(file->f_mode & FMODE_WRITE))
+	struct inode *inode = file->f_dentry->d_inode;
+	if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
 		return mnt_want_write(file->f_path.mnt);
 	else
 		return mnt_clone_write(file->f_path.mnt);
_
--
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