[S390] subchannel register/unregister mutex.

Add a reg_mutex to prevent unregistering a subchannel before it has been
registered. Since 2.6.17, we've seen oopses in kslowcrw when a device is
found to be not operational during sense id when doing initial device
recognition; it is not clear yet why that particular problem was not (yet)
observed with earlier kernels...

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 21 insertions, 3 deletions

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 1d3be80797f8..a09deea5d687 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -108,6 +108,24 @@ css_subchannel_release(struct device *dev)
 
 extern int css_get_ssd_info(struct subchannel *sch);
 
+
+int css_sch_device_register(struct subchannel *sch)
+{
+        int ret;
+
+        mutex_lock(&sch->reg_mutex);
+        ret = device_register(&sch->dev);
+        mutex_unlock(&sch->reg_mutex);
+        return ret;
+}
+
+void css_sch_device_unregister(struct subchannel *sch)
+{
+        mutex_lock(&sch->reg_mutex);
+        device_unregister(&sch->dev);
+        mutex_unlock(&sch->reg_mutex);
+}
+
 static int
 css_register_subchannel(struct subchannel *sch)
 {
@@ -119,7 +137,7 @@ css_register_subchannel(struct subchannel *sch)
         sch->dev.release = &css_subchannel_release;
         
         /* make it known to the system */
-        ret = device_register(&sch->dev);
+        ret = css_sch_device_register(sch);
         if (ret)
                 printk (KERN_WARNING "%s: could not register %s\n",
                         __func__, sch->dev.bus_id);
@@ -250,7 +268,7 @@ css_evaluate_subchannel(struct subchannel_id schid, int slow)
                  * The device will be killed automatically.
                  */
                 cio_disable_subchannel(sch);
-                device_unregister(&sch->dev);
+                css_sch_device_unregister(sch);
                 /* Reset intparm to zeroes. */
                 sch->schib.pmcw.intparm = 0;
                 cio_modify(sch);
@@ -264,7 +282,7 @@ css_evaluate_subchannel(struct subchannel_id schid, int slow)
                  * away in any case.
                  */
                 if (!disc) {
-                        device_unregister(&sch->dev);
+                        css_sch_device_unregister(sch);
                         /* Reset intparm to zeroes. */
                         sch->schib.pmcw.intparm = 0;
                         cio_modify(sch);