[S390] etr/stp: fix possible deadlock

Precreate stop_machine threads in case the machine supports ETR/STP.
Otherwise we might deadlock if a time sync operation gets scheduled
and the creation of stop_machine threads would cause disk I/O.
This is just the minimal fix.
The real fix would be to only precreate stop_machine threads if
ETR/STP is actually used. But that would be a rather large and
complicated patch.

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

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index d649600..fc468ca 100644 (file)
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -399,8 +399,10 @@ static struct workqueue_struct *time_sync_wq;
 
 static void __init time_init_wq(void)
 {
-       if (!time_sync_wq)
-               time_sync_wq = create_singlethread_workqueue("timesync");
+       if (time_sync_wq)
+               return;
+       time_sync_wq = create_singlethread_workqueue("timesync");
+       stop_machine_create();
 }
 
 /*