From: Alexey Dobriyan <adobriyan@gmail.com>

If ->open() wasn't called, returning 0 is misleading and, theoretically,
oopsable:
1. remove_proc_entry clears ->proc_fops, drops lock,
2. ->open "succeeds",
3. ->release oopses, because it assumes ->open was called (single_release()).

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN fs/proc/inode.c~proc-fix-return-value-of-proc_reg_open-in-too-late-case fs/proc/inode.c
--- a/fs/proc/inode.c~proc-fix-return-value-of-proc_reg_open-in-too-late-case
+++ a/fs/proc/inode.c
@@ -350,7 +350,7 @@ static int proc_reg_open(struct inode *i
 	if (!pde->proc_fops) {
 		spin_unlock(&pde->pde_unload_lock);
 		kfree(pdeo);
-		return rv;
+		return -EINVAL;
 	}
 	pde->pde_users++;
 	open = pde->proc_fops->open;
_