md: only count actual openers as access which prevent a 'stop'

Open isn't the only thing that increments ->active.  e.g. reading
/proc/mdstat will increment it briefly.  So to avoid false positives
in testing for concurrent access, introduce a new counter that counts
just the number of times the md device it open.

Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 8 insertions, 4 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 4bfbc1982cda..450f30b6edf9 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -273,6 +273,7 @@ static mddev_t * mddev_find(dev_t unit)
         INIT_LIST_HEAD(&new->all_mddevs);
         init_timer(&new->safemode_timer);
         atomic_set(&new->active, 1);
+        atomic_set(&new->openers, 0);
         spin_lock_init(&new->write_lock);
         init_waitqueue_head(&new->sb_wait);
         init_waitqueue_head(&new->recovery_wait);
@@ -2695,14 +2696,14 @@ array_state_store(mddev_t *mddev, const char *buf, size_t len)
                 break;
         case clear:
                 /* stopping an active array */
-                if (atomic_read(&mddev->active) > 1)
+                if (atomic_read(&mddev->openers) > 0)
                         return -EBUSY;
                 err = do_md_stop(mddev, 0, 0);
                 break;
         case inactive:
                 /* stopping an active array */
                 if (mddev->pers) {
-                        if (atomic_read(&mddev->active) > 1)
+                        if (atomic_read(&mddev->openers) > 0)
                                 return -EBUSY;
                         err = do_md_stop(mddev, 2, 0);
                 } else
@@ -3816,7 +3817,7 @@ static int do_md_stop(mddev_t * mddev, int mode, int is_open)
         int err = 0;
         struct gendisk *disk = mddev->gendisk;
 
-        if (atomic_read(&mddev->active) > 1 + is_open) {
+        if (atomic_read(&mddev->openers) > is_open) {
                 printk("md: %s still in use.\n",mdname(mddev));
                 return -EBUSY;
         }
@@ -5014,6 +5015,7 @@ static int md_open(struct inode *inode, struct file *file)
 
         err = 0;
         mddev_get(mddev);
+        atomic_inc(&mddev->openers);
         mddev_unlock(mddev);
 
         check_disk_change(inode->i_bdev);
@@ -5026,6 +5028,7 @@ static int md_release(struct inode *inode, struct file * file)
         mddev_t *mddev = inode->i_bdev->bd_disk->private_data;
 
         BUG_ON(!mddev);
+        atomic_dec(&mddev->openers);
         mddev_put(mddev);
 
         return 0;
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 6f72b47ae41c..4bef4791d80d 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -215,7 +215,8 @@ struct mddev_s
 
         int                             in_sync;        /* know to not need resync */
         struct mutex                    reconfig_mutex;
-        atomic_t                        active;
+        atomic_t                        active;         /* general refcount */
+        atomic_t                        openers;        /* number of active opens */
 
         int                             changed;        /* true if we might need to reread partition info */
         int                             degraded;       /* whether md should consider