[S390] cio/crw: add/fix locking

The crw_unregister_handler uses xchg + synchronize_sched when
unregistering a crw_handler.
This doesn't protect crw_collect_info to potentially jump to NULL since
it has unlocked code like this:

if (crw_handlers[i])
        crw_handlers[i](NULL, NULL, 1);

So add a mutex which protects the crw handler array for changes.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/drivers/s390/cio/crw.c b/drivers/s390/cio/crw.c
index 508f88f..d157665 100644 (file)
--- a/drivers/s390/cio/crw.c
+++ b/drivers/s390/cio/crw.c
@@ -9,11 +9,13 @@
  */
 
 #include <linux/semaphore.h>
+#include <linux/mutex.h>
 #include <linux/kthread.h>
 #include <linux/init.h>
 #include <asm/crw.h>
 
 static struct semaphore crw_semaphore;
+static DEFINE_MUTEX(crw_handler_mutex);
 static crw_handler_t crw_handlers[NR_RSCS];
 
 /**
@@ -25,11 +27,17 @@ static crw_handler_t crw_handlers[NR_RSCS];
  */
 int crw_register_handler(int rsc, crw_handler_t handler)
 {
+       int rc = 0;
+
        if ((rsc < 0) || (rsc >= NR_RSCS))
                return -EINVAL;
-       if (!cmpxchg(&crw_handlers[rsc], NULL, handler))
-               return 0;
-       return -EBUSY;
+       mutex_lock(&crw_handler_mutex);
+       if (crw_handlers[rsc])
+               rc = -EBUSY;
+       else
+               crw_handlers[rsc] = handler;
+       mutex_unlock(&crw_handler_mutex);
+       return rc;
 }
 
 /**
@@ -40,8 +48,9 @@ void crw_unregister_handler(int rsc)
 {
        if ((rsc < 0) || (rsc >= NR_RSCS))
                return;
-       xchg(&crw_handlers[rsc], NULL);
-       synchronize_sched();
+       mutex_lock(&crw_handler_mutex);
+       crw_handlers[rsc] = NULL;
+       mutex_unlock(&crw_handler_mutex);
 }
 
 /*
@@ -58,6 +67,8 @@ repeat:
        ignore = down_interruptible(&crw_semaphore);
        chain = 0;
        while (1) {
+               crw_handler_t handler;
+
                if (unlikely(chain > 1)) {
                        struct crw tmp_crw;
 
@@ -90,10 +101,12 @@ repeat:
                        int i;
 
                        pr_debug("%s: crw overflow detected!\n", __func__);
+                       mutex_lock(&crw_handler_mutex);
                        for (i = 0; i < NR_RSCS; i++) {
                                if (crw_handlers[i])
                                        crw_handlers[i](NULL, NULL, 1);
                        }
+                       mutex_unlock(&crw_handler_mutex);
                        chain = 0;
                        continue;
                }
@@ -101,10 +114,11 @@ repeat:
                        chain++;
                        continue;
                }
-               if (crw_handlers[crw[chain].rsc])
-                       crw_handlers[crw[chain].rsc](&crw[0],
-                                                    chain ? &crw[1] : NULL,
-                                                    0);
+               mutex_lock(&crw_handler_mutex);
+               handler = crw_handlers[crw[chain].rsc];
+               if (handler)
+                       handler(&crw[0], chain ? &crw[1] : NULL, 0);
+               mutex_unlock(&crw_handler_mutex);
                /* chain is always 0 or 1 here. */
                chain = crw[chain].chn ? chain + 1 : 0;
        }