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>

2 files changed, 1 insertions, 5 deletions

diff --git a/include/linux/ipmi_smi.h b/include/linux/ipmi_smi.h
index 62b7366..f7c9c75 100644
--- a/include/linux/ipmi_smi.h
+++ b/include/linux/ipmi_smi.h
@@ -230,6 +230,6 @@ static inline void ipmi_free_smi_msg(struct ipmi_smi_msg *msg)
    automatically be dstroyed when the interface is destroyed. */
 int ipmi_smi_add_proc_entry(ipmi_smi_t smi, char *name,
 			    read_proc_t *read_proc,
-			    void *data, struct module *owner);
+			    void *data);
 
 #endif /* __LINUX_IPMI_SMI_H */
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index b8bdb96..fbfa3d4 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;