[PATCH] powerpc/pseries: mutex lock to serialize EEH event processing

This forces the processing of EEH PCI events to be serialized,
using a very simple mutex lock. This serialization is required to
avoid races involving additional PCI device failures that may occur
during the recovery phase of a previous failure.
Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/pseries/eeh_event.c

@@ -19,7 +19,9 @@
  */
 
 #include <linux/list.h>
+#include <linux/mutex.h>
 #include <linux/pci.h>
+#include <linux/workqueue.h>
 #include <asm/eeh_event.h>
 #include <asm/ppc-pci.h>
 
@@ -37,14 +39,18 @@ LIST_HEAD(eeh_eventlist);
 static void eeh_thread_launcher(void *);
 DECLARE_WORK(eeh_event_wq, eeh_thread_launcher, NULL);
 
+/* Serialize reset sequences for a given pci device */
+DEFINE_MUTEX(eeh_event_mutex);
+
 /**
- * eeh_event_handler - dispatch EEH events.  The detection of a frozen
- * slot can occur inside an interrupt, where it can be hard to do
- * anything about it.  The goal of this routine is to pull these
- * detection events out of the context of the interrupt handler, and
- * re-dispatch them for processing at a later time in a normal context.
- *
+ * eeh_event_handler - dispatch EEH events.
  * @dummy - unused
+ *
+ * The detection of a frozen slot can occur inside an interrupt,
+ * where it can be hard to do anything about it.  The goal of this
+ * routine is to pull these detection events out of the context
+ * of the interrupt handler, and re-dispatch them for processing
+ * at a later time in a normal context.
  */
 static int eeh_event_handler(void * dummy)
 {
@@ -64,23 +70,24 @@ static int eeh_event_handler(void * dummy)
 			event = list_entry(eeh_eventlist.next, struct eeh_event, list);
 			list_del(&event->list);
 		}
-		
-		if (event)
-			eeh_mark_slot(event->dn, EEH_MODE_RECOVERING);
-
 		spin_unlock_irqrestore(&eeh_eventlist_lock, flags);
+
 		if (event == NULL)
 			break;
 
+		/* Serialize processing of EEH events */
+		mutex_lock(&eeh_event_mutex);
+		eeh_mark_slot(event->dn, EEH_MODE_RECOVERING);
+
 		printk(KERN_INFO "EEH: Detected PCI bus error on device %s\n",
 		       pci_name(event->dev));
 
 		handle_eeh_events(event);
 
 		eeh_clear_slot(event->dn, EEH_MODE_RECOVERING);
-
 		pci_dev_put(event->dev);
 		kfree(event);
+		mutex_unlock(&eeh_event_mutex);
 	}
 
 	return 0;
@@ -88,7 +95,6 @@ static int eeh_event_handler(void * dummy)
 
 /**
  * eeh_thread_launcher
- *
  * @dummy - unused
  */
 static void eeh_thread_launcher(void *dummy)