[S390] vmur: Use wait queue instead of mutex to serialize open

If user space opens a unit record device node then vmur is leaving the kernel
with lock open_mutex still held to prevent other processes from opening the
device simultaneously. This causes lockdep to complain about a lock held when
returning to user space.
Now the mutex is replaced by a wait queue to serialize device open.

Signed-off-by: Frank Munzert <munzert@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

2 files changed, 20 insertions, 8 deletions

diff --git a/drivers/s390/char/vmur.c b/drivers/s390/char/vmur.c
index 7689b500a104..83ae9a852f00 100644
--- a/drivers/s390/char/vmur.c
+++ b/drivers/s390/char/vmur.c
@@ -100,7 +100,8 @@ static struct urdev *urdev_alloc(struct ccw_device *cdev)
         urd->reclen = cdev->id.driver_info;
         ccw_device_get_id(cdev, &urd->dev_id);
         mutex_init(&urd->io_mutex);
-        mutex_init(&urd->open_mutex);
+        init_waitqueue_head(&urd->wait);
+        spin_lock_init(&urd->open_lock);
         atomic_set(&urd->ref_count,  1);
         urd->cdev = cdev;
         get_device(&cdev->dev);
@@ -678,17 +679,21 @@ static int ur_open(struct inode *inode, struct file *file)
         if (!urd)
                 return -ENXIO;
 
-        if (file->f_flags & O_NONBLOCK) {
-                if (!mutex_trylock(&urd->open_mutex)) {
+        spin_lock(&urd->open_lock);
+        while (urd->open_flag) {
+                spin_unlock(&urd->open_lock);
+                if (file->f_flags & O_NONBLOCK) {
                         rc = -EBUSY;
                         goto fail_put;
                 }
-        } else {
-                if (mutex_lock_interruptible(&urd->open_mutex)) {
+                if (wait_event_interruptible(urd->wait, urd->open_flag == 0)) {
                         rc = -ERESTARTSYS;
                         goto fail_put;
                 }
+                spin_lock(&urd->open_lock);
         }
+        urd->open_flag++;
+        spin_unlock(&urd->open_lock);
 
         TRACE("ur_open\n");
 
@@ -720,7 +725,9 @@ static int ur_open(struct inode *inode, struct file *file)
 fail_urfile_free:
         urfile_free(urf);
 fail_unlock:
-        mutex_unlock(&urd->open_mutex);
+        spin_lock(&urd->open_lock);
+        urd->open_flag--;
+        spin_unlock(&urd->open_lock);
 fail_put:
         urdev_put(urd);
         return rc;
@@ -731,7 +738,10 @@ static int ur_release(struct inode *inode, struct file *file)
         struct urfile *urf = file->private_data;
 
         TRACE("ur_release\n");
-        mutex_unlock(&urf->urd->open_mutex);
+        spin_lock(&urf->urd->open_lock);
+        urf->urd->open_flag--;
+        spin_unlock(&urf->urd->open_lock);
+        wake_up_interruptible(&urf->urd->wait);
         urdev_put(urf->urd);
         urfile_free(urf);
         return 0;
diff --git a/drivers/s390/char/vmur.h b/drivers/s390/char/vmur.h
index fa959644735a..fa320ad4593d 100644
--- a/drivers/s390/char/vmur.h
+++ b/drivers/s390/char/vmur.h
@@ -62,7 +62,6 @@ struct file_control_block {
 struct urdev {
         struct ccw_device *cdev;        /* Backpointer to ccw device */
         struct mutex io_mutex;          /* Serialises device IO */
-        struct mutex open_mutex;        /* Serialises access to device */
         struct completion *io_done;     /* do_ur_io waits; irq completes */
         struct device *device;
         struct cdev *char_device;
@@ -71,6 +70,9 @@ struct urdev {
         int class;                      /* VM device class */
         int io_request_rc;              /* return code from I/O request */
         atomic_t ref_count;             /* reference counter */
+        wait_queue_head_t wait;         /* wait queue to serialize open */
+        int open_flag;                  /* "urdev is open" flag */
+        spinlock_t open_lock;           /* serialize critical sections */
 };
 
 /*