[PATCH] r/o bind mounts: make access() use new r/o helper

It is OK to let access() go without using a mnt_want/drop_write() pair because
it doesn't actually do writes to the filesystem, and it is inherently racy
anyway.  This is a rare case when it is OK to use __mnt_is_readonly()
directly.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/open.c b/fs/open.c
index 4d690e33446f854f960645a1b57258e133dd5e11..e58382d57e721cf3f381c7c49edb03d547d75135 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -459,8 +459,17 @@ asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode)
        if(res || !(mode & S_IWOTH) ||
           special_file(nd.path.dentry->d_inode->i_mode))
                goto out_path_release;
-
-       if(IS_RDONLY(nd.path.dentry->d_inode))
+       /*
+        * This is a rare case where using __mnt_is_readonly()
+        * is OK without a mnt_want/drop_write() pair.  Since
+        * no actual write to the fs is performed here, we do
+        * not need to telegraph to that to anyone.
+        *
+        * By doing this, we accept that this access is
+        * inherently racy and know that the fs may change
+        * state before we even see this result.
+        */
+       if (__mnt_is_readonly(nd.path.mnt))
                res = -EROFS;
 
 out_path_release: