[S390] monwriter: Serialization bug for multithreaded applications.

Locking added so that multithreaded applications can now do writes
from different threads without the risk of storage corruption.

Signed-off-by: Melissa Howland <melissah@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/drivers/s390/char/monwriter.c b/drivers/s390/char/monwriter.c
index 268598ef3efe9ada78e23881b416ce6ef933b44e..20442fbf93465087b266f21d6790a71f9df8fa83 100644 (file)
--- 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;
 }