[S390] dasd: fix race in dasd timer handling

In dasd_device_set_timer and dasd_block_set_timer we interpret the
return value of mod_timer in a wrong way. If the timer expires in
the small window between our check of timer_pending and the call to
mod_timer, then the timer will be set, mod_timer returns zero and
we will call add_timer for a timer that is already pending.
As del_timer and mod_timer do all the necessary checking themselves,
we can simplify our code and remove the race a the same time.

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 16 insertions, 30 deletions

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index bd5914994142..08c23a921012 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -57,6 +57,8 @@ static void dasd_device_tasklet(struct dasd_device *);
 static void dasd_block_tasklet(struct dasd_block *);
 static void do_kick_device(struct work_struct *);
 static void dasd_return_cqr_cb(struct dasd_ccw_req *, void *);
+static void dasd_device_timeout(unsigned long);
+static void dasd_block_timeout(unsigned long);
 
 /*
  * SECTION: Operations on the device structure.
@@ -99,6 +101,8 @@ struct dasd_device *dasd_alloc_device(void)
                      (unsigned long) device);
         INIT_LIST_HEAD(&device->ccw_queue);
         init_timer(&device->timer);
+        device->timer.function = dasd_device_timeout;
+        device->timer.data = (unsigned long) device;
         INIT_WORK(&device->kick_work, do_kick_device);
         device->state = DASD_STATE_NEW;
         device->target = DASD_STATE_NEW;
@@ -138,6 +142,8 @@ struct dasd_block *dasd_alloc_block(void)
         INIT_LIST_HEAD(&block->ccw_queue);
         spin_lock_init(&block->queue_lock);
         init_timer(&block->timer);
+        block->timer.function = dasd_block_timeout;
+        block->timer.data = (unsigned long) block;
 
         return block;
 }
@@ -915,19 +921,10 @@ static void dasd_device_timeout(unsigned long ptr)
  */
 void dasd_device_set_timer(struct dasd_device *device, int expires)
 {
-        if (expires == 0) {
-                if (timer_pending(&device->timer))
-                        del_timer(&device->timer);
-                return;
-        }
-        if (timer_pending(&device->timer)) {
-                if (mod_timer(&device->timer, jiffies + expires))
-                        return;
-        }
-        device->timer.function = dasd_device_timeout;
-        device->timer.data = (unsigned long) device;
-        device->timer.expires = jiffies + expires;
-        add_timer(&device->timer);
+        if (expires == 0)
+                del_timer(&device->timer);
+        else
+                mod_timer(&device->timer, jiffies + expires);
 }
 
 /*
@@ -935,8 +932,7 @@ void dasd_device_set_timer(struct dasd_device *device, int expires)
  */
 void dasd_device_clear_timer(struct dasd_device *device)
 {
-        if (timer_pending(&device->timer))
-                del_timer(&device->timer);
+        del_timer(&device->timer);
 }
 
 static void dasd_handle_killed_request(struct ccw_device *cdev,
@@ -1586,19 +1582,10 @@ static void dasd_block_timeout(unsigned long ptr)
  */
 void dasd_block_set_timer(struct dasd_block *block, int expires)
 {
-        if (expires == 0) {
-                if (timer_pending(&block->timer))
-                        del_timer(&block->timer);
-                return;
-        }
-        if (timer_pending(&block->timer)) {
-                if (mod_timer(&block->timer, jiffies + expires))
-                        return;
-        }
-        block->timer.function = dasd_block_timeout;
-        block->timer.data = (unsigned long) block;
-        block->timer.expires = jiffies + expires;
-        add_timer(&block->timer);
+        if (expires == 0)
+                del_timer(&block->timer);
+        else
+                mod_timer(&block->timer, jiffies + expires);
 }
 
 /*
@@ -1606,8 +1593,7 @@ void dasd_block_set_timer(struct dasd_block *block, int expires)
  */
 void dasd_block_clear_timer(struct dasd_block *block)
 {
-        if (timer_pending(&block->timer))
-                del_timer(&block->timer);
+        del_timer(&block->timer);
 }
 
 /*