---

yaml
---
r: 165874
b: refs/heads/master
c: 4504230
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4fadd7bb20a1e7c774ed88dc703d8fbcd00ff917
+refs/heads/master: 4504230a71566785a05d3e6b53fa1ee071b864eb

trunk/fs/block_dev.c

@@ -230,43 +230,54 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 	int error = 0;
 
 	mutex_lock(&bdev->bd_fsfreeze_mutex);
-	if (bdev->bd_fsfreeze_count > 0) {
-		bdev->bd_fsfreeze_count++;
+	if (++bdev->bd_fsfreeze_count > 1) {
+		/*
+		 * We don't even need to grab a reference - the first call
+		 * to freeze_bdev grab an active reference and only the last
+		 * thaw_bdev drops it.
+		 */
 		sb = get_super(bdev);
+		drop_super(sb);
 		mutex_unlock(&bdev->bd_fsfreeze_mutex);
 		return sb;
 	}
-	bdev->bd_fsfreeze_count++;
-
-	sb = get_super(bdev);
-	if (sb && !(sb->s_flags & MS_RDONLY)) {
-		sb->s_frozen = SB_FREEZE_WRITE;
-		smp_wmb();
-
-		sync_filesystem(sb);
-
-		sb->s_frozen = SB_FREEZE_TRANS;
-		smp_wmb();
-
-		sync_blockdev(sb->s_bdev);
-
-		if (sb->s_op->freeze_fs) {
-			error = sb->s_op->freeze_fs(sb);
-			if (error) {
-				printk(KERN_ERR
-					"VFS:Filesystem freeze failed\n");
-				sb->s_frozen = SB_UNFROZEN;
-				drop_super(sb);
-				bdev->bd_fsfreeze_count--;
-				mutex_unlock(&bdev->bd_fsfreeze_mutex);
-				return ERR_PTR(error);
-			}
+
+	sb = get_active_super(bdev);
+	if (!sb)
+		goto out;
+	if (sb->s_flags & MS_RDONLY) {
+		deactivate_locked_super(sb);
+		mutex_unlock(&bdev->bd_fsfreeze_mutex);
+		return sb;
+	}
+
+	sb->s_frozen = SB_FREEZE_WRITE;
+	smp_wmb();
+
+	sync_filesystem(sb);
+
+	sb->s_frozen = SB_FREEZE_TRANS;
+	smp_wmb();
+
+	sync_blockdev(sb->s_bdev);
+
+	if (sb->s_op->freeze_fs) {
+		error = sb->s_op->freeze_fs(sb);
+		if (error) {
+			printk(KERN_ERR
+				"VFS:Filesystem freeze failed\n");
+			sb->s_frozen = SB_UNFROZEN;
+			deactivate_locked_super(sb);
+			bdev->bd_fsfreeze_count--;
+			mutex_unlock(&bdev->bd_fsfreeze_mutex);
+			return ERR_PTR(error);
 		}
 	}
+	up_write(&sb->s_umount);
 
+ out:
 	sync_blockdev(bdev);
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
-
 	return sb;	/* thaw_bdev releases s->s_umount */
 }
 EXPORT_SYMBOL(freeze_bdev);
@@ -280,43 +291,44 @@ EXPORT_SYMBOL(freeze_bdev);
  */
 int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
-	int error = 0;
+	int error = -EINVAL;
 
 	mutex_lock(&bdev->bd_fsfreeze_mutex);
-	if (!bdev->bd_fsfreeze_count) {
-		mutex_unlock(&bdev->bd_fsfreeze_mutex);
-		return -EINVAL;
-	}
-
-	bdev->bd_fsfreeze_count--;
-	if (bdev->bd_fsfreeze_count > 0) {
-		if (sb)
-			drop_super(sb);
-		mutex_unlock(&bdev->bd_fsfreeze_mutex);
-		return 0;
-	}
-
-	if (sb) {
-		BUG_ON(sb->s_bdev != bdev);
-		if (!(sb->s_flags & MS_RDONLY)) {
-			if (sb->s_op->unfreeze_fs) {
-				error = sb->s_op->unfreeze_fs(sb);
-				if (error) {
-					printk(KERN_ERR
-						"VFS:Filesystem thaw failed\n");
-					sb->s_frozen = SB_FREEZE_TRANS;
-					bdev->bd_fsfreeze_count++;
-					mutex_unlock(&bdev->bd_fsfreeze_mutex);
-					return error;
-				}
-			}
-			sb->s_frozen = SB_UNFROZEN;
-			smp_wmb();
-			wake_up(&sb->s_wait_unfrozen);
+	if (!bdev->bd_fsfreeze_count)
+		goto out_unlock;
+
+	error = 0;
+	if (--bdev->bd_fsfreeze_count > 0)
+		goto out_unlock;
+
+	if (!sb)
+		goto out_unlock;
+
+	BUG_ON(sb->s_bdev != bdev);
+	down_write(&sb->s_umount);
+	if (sb->s_flags & MS_RDONLY)
+		goto out_deactivate;
+
+	if (sb->s_op->unfreeze_fs) {
+		error = sb->s_op->unfreeze_fs(sb);
+		if (error) {
+			printk(KERN_ERR
+				"VFS:Filesystem thaw failed\n");
+			sb->s_frozen = SB_FREEZE_TRANS;
+			bdev->bd_fsfreeze_count++;
+			mutex_unlock(&bdev->bd_fsfreeze_mutex);
+			return error;
 		}
-		drop_super(sb);
 	}
 
+	sb->s_frozen = SB_UNFROZEN;
+	smp_wmb();
+	wake_up(&sb->s_wait_unfrozen);
+
+out_deactivate:
+	if (sb)
+		deactivate_locked_super(sb);
+out_unlock:
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
 	return 0;
 }

trunk/fs/super.c

@@ -465,6 +465,48 @@ struct super_block * get_super(struct block_device *bdev)
 }
 
 EXPORT_SYMBOL(get_super);
+
+/**
+ * get_active_super - get an active reference to the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given.  Returns the superblock with an active
+ * reference and s_umount held exclusively or %NULL if none was found.
+ */
+struct super_block *get_active_super(struct block_device *bdev)
+{
+	struct super_block *sb;
+
+	if (!bdev)
+		return NULL;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (sb->s_bdev != bdev)
+			continue;
+
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+		down_write(&sb->s_umount);
+		if (sb->s_root) {
+			spin_lock(&sb_lock);
+			if (sb->s_count > S_BIAS) {
+				atomic_inc(&sb->s_active);
+				sb->s_count--;
+				spin_unlock(&sb_lock);
+				return sb;
+			}
+			spin_unlock(&sb_lock);
+		}
+		up_write(&sb->s_umount);
+		put_super(sb);
+		yield();
+		spin_lock(&sb_lock);
+	}
+	spin_unlock(&sb_lock);
+	return NULL;
+}
 
 struct super_block * user_get_super(dev_t dev)
 {
@@ -527,11 +569,15 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 {
 	int retval;
 	int remount_rw;
-
+
+	if (sb->s_frozen != SB_UNFROZEN)
+		return -EBUSY;
+
 #ifdef CONFIG_BLOCK
 	if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
 		return -EACCES;
 #endif
+
 	if (flags & MS_RDONLY)
 		acct_auto_close(sb);
 	shrink_dcache_sb(sb);

trunk/include/linux/fs.h

@@ -2334,6 +2334,7 @@ extern void get_filesystem(struct file_system_type *fs);
 extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_active_super(struct block_device *bdev);
 extern struct super_block *user_get_super(dev_t);
 extern void drop_super(struct super_block *sb);