[PATCH 4/4] staging: dgnc: cleanup properly

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

dgnc_cleanup_module() was called when the module unloaded to do a total
cleanup and it was also called if pci_register_driver() fails. But
dgnc_cleanup_module() will try dgnc_remove_driver_sysfiles() but the
sysfiles will be created only if pci_register_driver() succeeds.
So if pci_register_driver() fails and we try dgnc_cleanup_module() then we
were getting:

[  942.001479] BUG: unable to handle kernel NULL pointer dereference at 00000018
[  942.001482] IP: [<c122c7a8>] sysfs_remove_file_ns+0x8/0x20

with part of the call trace as:

[  942.001544] Call Trace:
[  942.001555]  [<c149acc6>] driver_remove_file+0x16/0x20
[  942.001571]  [<f864a708>] dgnc_remove_driver_sysfiles+0x18/0x40 [dgnc]
[  942.001575]  [<f8643ac7>] dgnc_cleanup_module+0x47/0x260 [dgnc]
[  942.001577]  [<f86cb000>] ? 0xf86cb000
[  942.001580]  [<f86cb1e6>] dgnc_init_module+0x1e6/0x1000 [dgnc]

Lets have a separate cleanup function which will execute
dgnc_remove_driver_sysfiles() depending on the argument passed to it.

Reported-by: Navy Cheng <navych@126.com>
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
---

Hi Greg,
If you remember this problem was reported by Navy Cheng on the
kernelnewbies list but his report did not contain the call trace. He
just reported that his system hangs after reloading dgnc module.

 drivers/staging/dgnc/dgnc_driver.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/dgnc/dgnc_driver.c b/drivers/staging/dgnc/dgnc_driver.c
index 22a92d1..4eb410e 100644
--- a/drivers/staging/dgnc/dgnc_driver.c
+++ b/drivers/staging/dgnc/dgnc_driver.c
@@ -125,12 +125,7 @@ static struct pci_driver dgnc_driver = {
  *
  ************************************************************************/
 
-/*
- * dgnc_cleanup_module()
- *
- * Module unload.  This is where it all ends.
- */
-static void dgnc_cleanup_module(void)
+static void cleanup(bool sysfiles)
 {
 	int i;
 	unsigned long flags;
@@ -142,7 +137,8 @@ static void dgnc_cleanup_module(void)
 	/* Turn off poller right away. */
 	del_timer_sync(&dgnc_poll_timer);
 
-	dgnc_remove_driver_sysfiles(&dgnc_driver);
+	if (sysfiles)
+		dgnc_remove_driver_sysfiles(&dgnc_driver);
 
 	device_destroy(dgnc_class, MKDEV(dgnc_Major, 0));
 	class_destroy(dgnc_class);
@@ -155,7 +151,16 @@ static void dgnc_cleanup_module(void)
 	}
 
 	dgnc_tty_post_uninit();
+}
 
+/*
+ * dgnc_cleanup_module()
+ *
+ * Module unload.  This is where it all ends.
+ */
+static void dgnc_cleanup_module(void)
+{
+	cleanup(true);
 	pci_unregister_driver(&dgnc_driver);
 }
 
@@ -182,7 +187,7 @@ static int __init dgnc_init_module(void)
 	rc = pci_register_driver(&dgnc_driver);
 	if (rc) {
 		pr_warn("WARNING: dgnc driver load failed.  No Digi Neo or Classic boards found.\n");
-		dgnc_cleanup_module();
+		cleanup(false);
 		return rc;
 	}
 	dgnc_create_driver_sysfiles(&dgnc_driver);
-- 
1.9.1