Btrfs: disallow mutually exclusive admin operations from user mode

Btrfs admin operations that are manually started from user mode
and that cannot be executed at the same time return -EINPROGRESS.
A common way to enter and leave this locked section is introduced
since it used to be specific to the balance operation.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/ctree.h

@@ -1527,6 +1527,8 @@ struct btrfs_fs_info {
 
 	/* device replace state */
 	struct btrfs_dev_replace dev_replace;
+
+	atomic_t mutually_exclusive_operation_running;
 };
 
 /*

fs/btrfs/ioctl.c

@@ -1317,13 +1317,13 @@ static noinline int btrfs_ioctl_resize(struct btrfs_root *root,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	mutex_lock(&root->fs_info->volume_mutex);
-	if (root->fs_info->balance_ctl) {
-		printk(KERN_INFO "btrfs: balance in progress\n");
-		ret = -EINVAL;
-		goto out;
+	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+			1)) {
+		pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+		return -EINPROGRESS;
 	}
 
+	mutex_lock(&root->fs_info->volume_mutex);
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args)) {
 		ret = PTR_ERR(vol_args);
@@ -1419,6 +1419,7 @@ out_free:
 	kfree(vol_args);
 out:
 	mutex_unlock(&root->fs_info->volume_mutex);
+	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
 	return ret;
 }
 
@@ -2160,9 +2161,17 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 	if (btrfs_root_readonly(root))
 		return -EROFS;
 
+	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+			1)) {
+		pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+		return -EINPROGRESS;
+	}
 	ret = mnt_want_write_file(file);
-	if (ret)
+	if (ret) {
+		atomic_set(&root->fs_info->mutually_exclusive_operation_running,
+			   0);
 		return ret;
+	}
 
 	switch (inode->i_mode & S_IFMT) {
 	case S_IFDIR:
@@ -2214,6 +2223,7 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 	}
 out:
 	mnt_drop_write_file(file);
+	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
 	return ret;
 }
 
@@ -2225,13 +2235,13 @@ static long btrfs_ioctl_add_dev(struct btrfs_root *root, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	mutex_lock(&root->fs_info->volume_mutex);
-	if (root->fs_info->balance_ctl) {
-		printk(KERN_INFO "btrfs: balance in progress\n");
-		ret = -EINVAL;
-		goto out;
+	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+			1)) {
+		pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+		return -EINPROGRESS;
 	}
 
+	mutex_lock(&root->fs_info->volume_mutex);
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args)) {
 		ret = PTR_ERR(vol_args);
@@ -2244,6 +2254,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_root *root, void __user *arg)
 	kfree(vol_args);
 out:
 	mutex_unlock(&root->fs_info->volume_mutex);
+	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
 	return ret;
 }
 
@@ -2258,13 +2269,13 @@ static long btrfs_ioctl_rm_dev(struct btrfs_root *root, void __user *arg)
 	if (root->fs_info->sb->s_flags & MS_RDONLY)
 		return -EROFS;
 
-	mutex_lock(&root->fs_info->volume_mutex);
-	if (root->fs_info->balance_ctl) {
-		printk(KERN_INFO "btrfs: balance in progress\n");
-		ret = -EINVAL;
-		goto out;
+	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+			1)) {
+		pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+		return -EINPROGRESS;
 	}
 
+	mutex_lock(&root->fs_info->volume_mutex);
 	vol_args = memdup_user(arg, sizeof(*vol_args));
 	if (IS_ERR(vol_args)) {
 		ret = PTR_ERR(vol_args);
@@ -2277,6 +2288,7 @@ static long btrfs_ioctl_rm_dev(struct btrfs_root *root, void __user *arg)
 	kfree(vol_args);
 out:
 	mutex_unlock(&root->fs_info->volume_mutex);
+	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
 	return ret;
 }
 
@@ -3319,6 +3331,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	struct btrfs_ioctl_balance_args *bargs;
 	struct btrfs_balance_control *bctl;
 	int ret;
+	int need_to_clear_lock = 0;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -3354,10 +3367,13 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 		bargs = NULL;
 	}
 
-	if (fs_info->balance_ctl) {
+	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+			1)) {
+		pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
 		ret = -EINPROGRESS;
 		goto out_bargs;
 	}
+	need_to_clear_lock = 1;
 
 	bctl = kzalloc(sizeof(*bctl), GFP_NOFS);
 	if (!bctl) {
@@ -3391,6 +3407,9 @@ do_balance:
 out_bargs:
 	kfree(bargs);
 out:
+	if (need_to_clear_lock)
+		atomic_set(&root->fs_info->mutually_exclusive_operation_running,
+			   0);
 	mutex_unlock(&fs_info->balance_mutex);
 	mutex_unlock(&fs_info->volume_mutex);
 	mnt_drop_write_file(file);

fs/btrfs/volumes.c

@@ -2952,6 +2952,7 @@ static int balance_kthread(void *data)
 		ret = btrfs_balance(fs_info->balance_ctl, NULL);
 	}
 
+	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
 	mutex_unlock(&fs_info->balance_mutex);
 	mutex_unlock(&fs_info->volume_mutex);
 
@@ -2974,6 +2975,7 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
 		return 0;
 	}
 
+	WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
 	tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
 	if (IS_ERR(tsk))
 		return PTR_ERR(tsk);