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, 1 insertions, 9 deletions

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index 4c4214690dd1..fb73a52913a4 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -377,10 +377,6 @@ static const struct file_operations mtrr_fops = {
         .release = mtrr_close,
 };
 
-
-static struct proc_dir_entry *proc_root_mtrr;
-
-
 static int mtrr_seq_show(struct seq_file *seq, void *offset)
 {
         char factor;
@@ -423,11 +419,7 @@ static int __init mtrr_if_init(void)
             (!cpu_has(c, X86_FEATURE_CENTAUR_MCR)))
                 return -ENODEV;
 
-        proc_root_mtrr =
-                proc_create("mtrr", S_IWUSR | S_IRUGO, NULL, &mtrr_fops);
-
-        if (proc_root_mtrr)
-                proc_root_mtrr->owner = THIS_MODULE;
+        proc_create("mtrr", S_IWUSR | S_IRUGO, NULL, &mtrr_fops);
         return 0;
 }