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, 4 insertions, 8 deletions

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 7a88dfd..e93fc8d 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -1944,7 +1944,7 @@ static int stat_file_read_proc(char *page, char **start, off_t off,
 
 int ipmi_smi_add_proc_entry(ipmi_smi_t smi, char *name,
 			    read_proc_t *read_proc,
-			    void *data, struct module *owner)
+			    void *data)
 {
 	int                    rv = 0;
 #ifdef CONFIG_PROC_FS
@@ -1970,7 +1970,6 @@ int ipmi_smi_add_proc_entry(ipmi_smi_t smi, char *name,
 	} else {
 		file->data = data;
 		file->read_proc = read_proc;
-		file->owner = owner;
 
 		mutex_lock(&smi->proc_entry_lock);
 		/* Stick it on the list. */
@@ -1993,23 +1992,21 @@ static int add_proc_entries(ipmi_smi_t smi, int num)
 	smi->proc_dir = proc_mkdir(smi->proc_dir_name, proc_ipmi_root);
 	if (!smi->proc_dir)
 		rv = -ENOMEM;
-	else
-		smi->proc_dir->owner = THIS_MODULE;
 
 	if (rv == 0)
 		rv = ipmi_smi_add_proc_entry(smi, "stats",
 					     stat_file_read_proc,
-					     smi, THIS_MODULE);
+					     smi);
 
 	if (rv == 0)
 		rv = ipmi_smi_add_proc_entry(smi, "ipmb",
 					     ipmb_file_read_proc,
-					     smi, THIS_MODULE);
+					     smi);
 
 	if (rv == 0)
 		rv = ipmi_smi_add_proc_entry(smi, "version",
 					     version_file_read_proc,
-					     smi, THIS_MODULE);
+					     smi);
 #endif /* CONFIG_PROC_FS */
 
 	return rv;
@@ -4265,7 +4262,6 @@ static int ipmi_init_msghandler(void)
 	    return -ENOMEM;
 	}
 
-	proc_ipmi_root->owner = THIS_MODULE;
 #endif /* CONFIG_PROC_FS */
 
 	setup_timer(&ipmi_timer, ipmi_timeout, 0);