s390/ap: introduce mutex to lock the AP bus scan

Rework the invocations around ap_scan_bus():
- Protect ap_scan_bus() with a mutex to make sure only one
  scan at a time is running.
- The workqueue invocation which is triggered by either the
  module init or via AP bus scan timer expiration uses this
  mutex and if there is already a scan running, the work
  is simple aborted (as the job is done by another task).
- The ap_bus_force_rescan() which is invoked by higher level
  layers mostly on failures which indicate a bus scan may
  help is reworked to call ap_scan_bus() direct instead of
  enqueuing work into a system workqueue and waiting for that
  to finish. Of course the mutex is respected and in case of
  another task already running a bus scan the shortcut of
  waiting for this scan to finish and reusing the scan result
  is taken.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
index 2027baec995c5b25eeb315576cb2aba78fb15940..cce0bafd4c926a2bd53693545b505295dd9d425c 100644 (file)
--- a/drivers/s390/crypto/ap_bus.c
+++ b/drivers/s390/crypto/ap_bus.c
@@ -101,6 +101,9 @@ debug_info_t *ap_dbf_info;
 /*
  * AP bus rescan related things.
  */
+static bool ap_scan_bus(void);
+static bool ap_scan_bus_result; /* result of last ap_scan_bus() */
+static DEFINE_MUTEX(ap_scan_bus_mutex); /* mutex ap_scan_bus() invocations */
 static atomic64_t ap_scan_bus_count; /* counter ap_scan_bus() invocations */
 static int ap_scan_bus_time = AP_CONFIG_TIME;
 static struct timer_list ap_scan_bus_timer;
@@ -1011,16 +1014,47 @@ void ap_driver_unregister(struct ap_driver *ap_drv)
 }
 EXPORT_SYMBOL(ap_driver_unregister);
 
-void ap_bus_force_rescan(void)
+/*
+ * Enforce a synchronous AP bus rescan.
+ * Returns true if the bus scan finds a change in the AP configuration
+ * and AP devices have been added or deleted when this function returns.
+ */
+bool ap_bus_force_rescan(void)
 {
+       unsigned long scan_counter = atomic64_read(&ap_scan_bus_count);
+       bool rc = false;
+
+       pr_debug(">%s scan counter=%lu\n", __func__, scan_counter);
+
        /* Only trigger AP bus scans after the initial scan is done */
-       if (atomic64_read(&ap_scan_bus_count) <= 0)
-               return;
+       if (scan_counter <= 0)
+               goto out;
 
-       /* processing a asynchronous bus rescan */
-       del_timer(&ap_scan_bus_timer);
-       queue_work(system_long_wq, &ap_scan_bus_work);
-       flush_work(&ap_scan_bus_work);
+       /* Try to acquire the AP scan bus mutex */
+       if (mutex_trylock(&ap_scan_bus_mutex)) {
+               /* mutex acquired, run the AP bus scan */
+               ap_scan_bus_result = ap_scan_bus();
+               rc = ap_scan_bus_result;
+               mutex_unlock(&ap_scan_bus_mutex);
+               goto out;
+       }
+
+       /*
+        * Mutex acquire failed. So there is currently another task
+        * already running the AP bus scan. Then let's simple wait
+        * for the lock which means the other task has finished and
+        * stored the result in ap_scan_bus_result.
+        */
+       if (mutex_lock_interruptible(&ap_scan_bus_mutex)) {
+               /* some error occurred, ignore and go out */
+               goto out;
+       }
+       rc = ap_scan_bus_result;
+       mutex_unlock(&ap_scan_bus_mutex);
+
+out:
+       pr_debug("%s rc=%d\n", __func__, rc);
+       return rc;
 }
 EXPORT_SYMBOL(ap_bus_force_rescan);
 
@@ -2179,8 +2213,10 @@ static bool ap_config_has_new_doms(void)
 
 /**
  * ap_scan_bus(): Scan the AP bus for new devices
+ * Always run under mutex ap_scan_bus_mutex protection
+ * which needs to get locked/unlocked by the caller!
  * Returns true if any config change has been detected
- * otherwise false.
+ * during the scan, otherwise false.
  */
 static bool ap_scan_bus(void)
 {
@@ -2259,8 +2295,19 @@ static void ap_scan_bus_timer_callback(struct timer_list *unused)
  */
 static void ap_scan_bus_wq_callback(struct work_struct *unused)
 {
-       /* now finally do the AP bus scan */
-       ap_scan_bus();
+       /*
+        * Try to invoke an ap_scan_bus(). If the mutex acquisition
+        * fails there is currently another task already running the
+        * AP scan bus and there is no need to wait and re-trigger the
+        * scan again. Please note at the end of the scan bus function
+        * the AP scan bus timer is re-armed which triggers then the
+        * ap_scan_bus_timer_callback which enqueues a work into the
+        * system_long_wq which invokes this function here again.
+        */
+       if (mutex_trylock(&ap_scan_bus_mutex)) {
+               ap_scan_bus_result = ap_scan_bus();
+               mutex_unlock(&ap_scan_bus_mutex);
+       }
 }
 
 static int __init ap_debug_init(void)

diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h
index be320bd46f65742daf339954eff3afdeaae666eb..59c7ed49aa02489593ee052b543be348f7df3027 100644 (file)
--- a/drivers/s390/crypto/ap_bus.h
+++ b/drivers/s390/crypto/ap_bus.h
@@ -266,7 +266,7 @@ int ap_sb_available(void);
 bool ap_is_se_guest(void);
 void ap_wait(enum ap_sm_wait wait);
 void ap_request_timeout(struct timer_list *t);
-void ap_bus_force_rescan(void);
+bool ap_bus_force_rescan(void);
 
 int ap_test_config_usage_domain(unsigned int domain);
 int ap_test_config_ctrl_domain(unsigned int domain);