[S390] cio: wait for channel report

To fetch a pending channel report word (crw) we use a kernel
thread which triggers stcrw and sleeps on a semaphore. The s390
machine check handler uses crw_handle_channel_report to handle
one crw if needed.

This patch replaces the semaphore with a waitqueue (to block the
kernel thread) and an atomic_t (to count the number of pending
requests).

By this we achieve the ability to force this thread to check for
a pending crw (independent on when it is triggered by the machine
check handler) and wait for this action to finish.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 15 insertions, 14 deletions

diff --git a/drivers/s390/cio/crw.c b/drivers/s390/cio/crw.c
index d157665d0e76..425f741a280c 100644
--- a/drivers/s390/cio/crw.c
+++ b/drivers/s390/cio/crw.c
@@ -8,15 +8,16 @@
  *               Heiko Carstens <heiko.carstens@de.ibm.com>,
  */
 
-#include <linux/semaphore.h>
 #include <linux/mutex.h>
 #include <linux/kthread.h>
 #include <linux/init.h>
+#include <linux/wait.h>
 #include <asm/crw.h>
 
-static struct semaphore crw_semaphore;
 static DEFINE_MUTEX(crw_handler_mutex);
 static crw_handler_t crw_handlers[NR_RSCS];
+static atomic_t crw_nr_req = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(crw_handler_wait_q);
 
 /**
  * crw_register_handler() - register a channel report word handler
@@ -59,12 +60,14 @@ void crw_unregister_handler(int rsc)
 static int crw_collect_info(void *unused)
 {
         struct crw crw[2];
-        int ccode;
+        int ccode, signal;
         unsigned int chain;
-        int ignore;
 
 repeat:
-        ignore = down_interruptible(&crw_semaphore);
+        signal = wait_event_interruptible(crw_handler_wait_q,
+                                          atomic_read(&crw_nr_req) > 0);
+        if (unlikely(signal))
+                atomic_inc(&crw_nr_req);
         chain = 0;
         while (1) {
                 crw_handler_t handler;
@@ -122,25 +125,23 @@ repeat:
                 /* chain is always 0 or 1 here. */
                 chain = crw[chain].chn ? chain + 1 : 0;
         }
+        if (atomic_dec_and_test(&crw_nr_req))
+                wake_up(&crw_handler_wait_q);
         goto repeat;
         return 0;
 }
 
 void crw_handle_channel_report(void)
 {
-        up(&crw_semaphore);
+        atomic_inc(&crw_nr_req);
+        wake_up(&crw_handler_wait_q);
 }
 
-/*
- * Separate initcall needed for semaphore initialization since
- * crw_handle_channel_report might be called before crw_machine_check_init.
- */
-static int __init crw_init_semaphore(void)
+void crw_wait_for_channel_report(void)
 {
-        init_MUTEX_LOCKED(&crw_semaphore);
-        return 0;
+        crw_handle_channel_report();
+        wait_event(crw_handler_wait_q, atomic_read(&crw_nr_req) == 0);
 }
-pure_initcall(crw_init_semaphore);
 
 /*
  * Machine checks for the channel subsystem must be enabled