Commit eacf5b36 authored by Harald Freudenberger's avatar Harald Freudenberger Committed by Heiko Carstens
Browse files

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: default avatarHarald Freudenberger <freude@linux.ibm.com>
Reviewed-by: default avatarHolger Dengler <dengler@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent b5caf05e

drivers/s390/crypto/ap_bus.c

+57 −10
Original line number Diff line number Diff line
@@ -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)

drivers/s390/crypto/ap_bus.h

+1 −1
Original line number Diff line number Diff line
@@ -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);