vfs: mnt_want_write_file(): fix special file handling

I suspect 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?

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 277c28a63ead..7230787d18b0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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);