1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/s390/char/monwriter.c b/drivers/s390/char/monwriter.c
index 268598ef3efe..20442fbf9346 100644
--- a/drivers/s390/char/monwriter.c
+++ b/drivers/s390/char/monwriter.c
@@ -17,6 +17,7 @@
 #include <linux/miscdevice.h>
 #include <linux/ctype.h>
 #include <linux/poll.h>
+#include <linux/mutex.h>
 #include <asm/uaccess.h>
 #include <asm/ebcdic.h>
 #include <asm/io.h>
@@ -41,6 +42,7 @@ struct mon_private {
         size_t hdr_to_read;
         size_t data_to_read;
         struct mon_buf *current_buf;
+        struct mutex thread_mutex;
 };
 
 /*
@@ -179,6 +181,7 @@ static int monwrite_open(struct inode *inode, struct file *filp)
                 return -ENOMEM;
         INIT_LIST_HEAD(&monpriv->list);
         monpriv->hdr_to_read = sizeof(monpriv->hdr);
+        mutex_init(&monpriv->thread_mutex);
         filp->private_data = monpriv;
         return nonseekable_open(inode, filp);
 }
@@ -209,6 +212,7 @@ static ssize_t monwrite_write(struct file *filp, const char __user *data,
         void *to;
         int rc;
 
+        mutex_lock(&monpriv->thread_mutex);
         for (written = 0; written < count; ) {
                 if (monpriv->hdr_to_read) {
                         len = min(count - written, monpriv->hdr_to_read);
@@ -247,11 +251,13 @@ static ssize_t monwrite_write(struct file *filp, const char __user *data,
                 }
                 monpriv->hdr_to_read = sizeof(monpriv->hdr);
         }
+        mutex_unlock(&monpriv->thread_mutex);
         return written;
 
 out_error:
         monpriv->data_to_read = 0;
         monpriv->hdr_to_read = sizeof(struct monwrite_hdr);
+        mutex_unlock(&monpriv->thread_mutex);
         return rc;
 }