[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>

diff --git a/arch/s390/include/asm/crw.h b/arch/s390/include/asm/crw.h
index 2185a6d619d326b53e58f60ac928d35b782d8fd4..749a97e61bea0b014cc54639a1d8b9528e62f8c7 100644 (file)
--- a/arch/s390/include/asm/crw.h
+++ b/arch/s390/include/asm/crw.h
@@ -32,6 +32,7 @@ typedef void (*crw_handler_t)(struct crw *, struct crw *, int);
 extern int crw_register_handler(int rsc, crw_handler_t handler);
 extern void crw_unregister_handler(int rsc);
 extern void crw_handle_channel_report(void);
+void crw_wait_for_channel_report(void);
 
 #define NR_RSCS 16
 

diff --git a/drivers/s390/cio/crw.c b/drivers/s390/cio/crw.c
index d157665d0e761a1521d07dc9785ca4e799d4b704..425f741a280c4668ba17befa8762b4bd227fcb24 100644 (file)
--- 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