proc 2/2: remove struct proc_dir_entry::owner

Setting ->owner as done currently (pde->owner = THIS_MODULE) is racy
as correctly noted at bug #12454. Someone can lookup entry with NULL
->owner, thus not pinning enything, and release it later resulting
in module refcount underflow.

We can keep ->owner and supply it at registration time like ->proc_fops
and ->data.

But this leaves ->owner as easy-manipulative field (just one C assignment)
and somebody will forget to unpin previous/pin current module when
switching ->owner. ->proc_fops is declared as "const" which should give
some thoughts.

->read_proc/->write_proc were just fixed to not require ->owner for
protection.

rmmod'ed directories will be empty and return "." and ".." -- no harm.
And directories with tricky enough readdir and lookup shouldn't be modular.
We definitely don't want such modular code.

Removing ->owner will also make PDE smaller.

So, let's nuke it.

Kudos to Jeff Layton for reminding about this, let's say, oversight.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

1 files changed, 0 insertions, 4 deletions

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index b8bdb96eff78..fbfa3d44d33d 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -41,9 +41,6 @@ enum {
  * while parent/subdir create the directory structure (every
  * /proc file has a parent, but "subdir" is NULL for all
  * non-directory entries).
- *
- * "owner" is used to protect module
- * from unloading while proc_dir_entry is in use
  */
 
 typedef int (read_proc_t)(char *page, char **start, off_t off,
@@ -70,7 +67,6 @@ struct proc_dir_entry {
          * somewhere.
          */
         const struct file_operations *proc_fops;
-        struct module *owner;
         struct proc_dir_entry *next, *parent, *subdir;
         void *data;
         read_proc_t *read_proc;