debugfs: call debugfs_real_fops() only after debugfs_file_get()

The current implementation of debugfs_real_fops() relies on a
debugfs_fsdata instance to be installed at ->d_fsdata.

With future patches introducing lazy allocation of these, this requirement
will be guaranteed to be fullfilled only inbetween a
debugfs_file_get()/debugfs_file_put() pair.

The full proxies' fops implemented by debugfs happen to be the only
offenders. Fix them up by moving their debugfs_real_fops() calls past those
to debugfs_file_get().

full_proxy_release() is special as it doesn't invoke debugfs_file_get() at
all. Leave it alone for now.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 53f5c9a2af88..bc3549c95574 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -144,13 +144,13 @@ const struct file_operations debugfs_open_proxy_file_operations = {
 static ret_type full_proxy_ ## name(proto)                              \
 {                                                                       \
         struct dentry *dentry = F_DENTRY(filp);                 \
-        const struct file_operations *real_fops =                       \
-                debugfs_real_fops(filp);                                \
+        const struct file_operations *real_fops;                        \
         ret_type r;                                                     \
                                                                         \
         r = debugfs_file_get(dentry);                                   \
         if (unlikely(r))                                                \
                 return r;                                               \
+        real_fops = debugfs_real_fops(filp);                            \
         r = real_fops->name(args);                                      \
         debugfs_file_put(dentry);                                       \
         return r;                                                       \
@@ -177,13 +177,14 @@ FULL_PROXY_FUNC(unlocked_ioctl, long, filp,
 static unsigned int full_proxy_poll(struct file *filp,
                                 struct poll_table_struct *wait)
 {
-        const struct file_operations *real_fops = debugfs_real_fops(filp);
         struct dentry *dentry = F_DENTRY(filp);
         unsigned int r = 0;
+        const struct file_operations *real_fops;
 
         if (debugfs_file_get(dentry))
                 return POLLHUP;
 
+        real_fops = debugfs_real_fops(filp);
         r = real_fops->poll(filp, wait);
         debugfs_file_put(dentry);
         return r;