s390/cmm: avoid add_timer on concurrently used timer

cmm_set_timer could be called concurrently from cmm_thread, cmm proc
handler, upon cmm smsg receive and timer function itself. To avoid
potential race condition and hitting BUG_ON in add_timer on already
pending timer simply reuse mod_timer which is according to
documentation "the only safe way to modify the timeout" with multiple
unserialized concurrent users. mod_timer can handle both active and
inactive timers which allows to carry out minor code simplification as
well.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c
index 50d8d1c..510a182 100644 (file)
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -191,12 +191,7 @@ static void cmm_set_timer(void)
                        del_timer(&cmm_timer);
                return;
        }
-       if (timer_pending(&cmm_timer)) {
-               if (mod_timer(&cmm_timer, jiffies + cmm_timeout_seconds*HZ))
-                       return;
-       }
-       cmm_timer.expires = jiffies + cmm_timeout_seconds*HZ;
-       add_timer(&cmm_timer);
+       mod_timer(&cmm_timer, jiffies + cmm_timeout_seconds * HZ);
 }
 
 static void cmm_timer_fn(struct timer_list *unused)