[S390] vmur: Invalid allocation sequence for vmur class

The vmur class is allocated after the CCW driver is registered
and it is destroyed before the CCW driver is unregistered.
This is not the correct sequence, because the vmur class can be used
via driver core callbacks that are triggered during the CCW driver
deregistration. For Example:

1. vmur device is online
2. vmur module is unloaded

This leads to the following function call stack:

    <4> [<0000000000387286>] device_destroy+0x36/0x5c
    <4> [<000003e000209714>] ur_set_offline_force+0x9c/0x10c [vmur]
    <4> [<000003e00020a928>] ur_remove+0x64/0xbc [vmur]
    <4> [<00000000003e4d2e>] ccw_device_remove+0x42/0x1ac
    <4> [<000000000038a1aa>] __device_release_driver+0x9a/0xe4
    <4> [<000000000038a2da>] driver_detach+0xe6/0xec
    <4> [<0000000000388ee4>] bus_remove_driver+0xc0/0x108
    <4> [<000003e00020ad5a>] ur_exit+0x52/0x84 [vmur]

In device_destroy() the vmur class is used. Since it is already freed,
this can lead to a kernel panic.

To fix the problem, the vmur class has to be allocated before the CCW
driver is registered and destroyed after the CCW driver has ben unregistered.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/drivers/s390/char/vmur.c b/drivers/s390/char/vmur.c
index 31b902e94f7b6adf9ce952c0db6c19e3dfaa0c2c..77571b68539aff5afb8e2f70b0d9edb9ec5fc518 100644 (file)
--- a/drivers/s390/char/vmur.c
+++ b/drivers/s390/char/vmur.c
@@ -1026,9 +1026,15 @@ static int __init ur_init(void)
 
        debug_set_level(vmur_dbf, 6);
 
+       vmur_class = class_create(THIS_MODULE, "vmur");
+       if (IS_ERR(vmur_class)) {
+               rc = PTR_ERR(vmur_class);
+               goto fail_free_dbf;
+       }
+
        rc = ccw_driver_register(&ur_driver);
        if (rc)
-               goto fail_free_dbf;
+               goto fail_class_destroy;
 
        rc = alloc_chrdev_region(&dev, 0, NUM_MINORS, "vmur");
        if (rc) {
@@ -1038,18 +1044,13 @@ static int __init ur_init(void)
        }
        ur_first_dev_maj_min = MKDEV(MAJOR(dev), 0);
 
-       vmur_class = class_create(THIS_MODULE, "vmur");
-       if (IS_ERR(vmur_class)) {
-               rc = PTR_ERR(vmur_class);
-               goto fail_unregister_region;
-       }
        pr_info("%s loaded.\n", ur_banner);
        return 0;
 
-fail_unregister_region:
-       unregister_chrdev_region(ur_first_dev_maj_min, NUM_MINORS);
 fail_unregister_driver:
        ccw_driver_unregister(&ur_driver);
+fail_class_destroy:
+       class_destroy(vmur_class);
 fail_free_dbf:
        debug_unregister(vmur_dbf);
        return rc;
@@ -1057,9 +1058,9 @@ fail_free_dbf:
 
 static void __exit ur_exit(void)
 {
-       class_destroy(vmur_class);
        unregister_chrdev_region(ur_first_dev_maj_min, NUM_MINORS);
        ccw_driver_unregister(&ur_driver);
+       class_destroy(vmur_class);
        debug_unregister(vmur_dbf);
        pr_info("%s unloaded.\n", ur_banner);
 }