btrfs: track exclusive filesystem operation in flags

There are several operations, usually started from ioctls, that cannot
run concurrently. The status is tracked in
mutually_exclusive_operation_running as an atomic_t. We can easily track
the status as one of the per-filesystem flag bits with same
synchronization guarantees.

The conversion replaces:

* atomic_xchg(..., 1)    ->   test_and_set_bit(FLAG, ...)
* atomic_set(..., 0)     ->   clear_bit(FLAG, ...)
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -705,6 +705,11 @@ struct btrfs_delayed_root;
 #define BTRFS_FS_BTREE_ERR			11
 #define BTRFS_FS_LOG1_ERR			12
 #define BTRFS_FS_LOG2_ERR			13
+/*
+ * Indicate that a whole-filesystem exclusive operation is running
+ * (device replace, resize, device add/delete, balance)
+ */
+#define BTRFS_FS_EXCL_OP			14
 
 struct btrfs_fs_info {
 	u8 fsid[BTRFS_FSID_SIZE];
@@ -1070,8 +1075,6 @@ struct btrfs_fs_info {
 	/* device replace state */
 	struct btrfs_dev_replace dev_replace;
 
-	atomic_t mutually_exclusive_operation_running;
-
 	struct percpu_counter bio_counter;
 	wait_queue_head_t replace_wait;
 

fs/btrfs/dev-replace.c

@@ -784,8 +784,7 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
 	}
 	btrfs_dev_replace_unlock(dev_replace, 1);
 
-	WARN_ON(atomic_xchg(
-		&fs_info->mutually_exclusive_operation_running, 1));
+	WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
 	task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");
 	return PTR_ERR_OR_ZERO(task);
 }
@@ -814,7 +813,7 @@ static int btrfs_dev_replace_kthread(void *data)
 			(unsigned int)progress);
 	}
 	btrfs_dev_replace_continue_on_mount(fs_info);
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 
 	return 0;
 }

fs/btrfs/ioctl.c

@@ -1504,7 +1504,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 	if (ret)
 		return ret;
 
-	if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
 		mnt_drop_write_file(file);
 		return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 	}
@@ -1619,7 +1619,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 	kfree(vol_args);
 out:
 	mutex_unlock(&fs_info->volume_mutex);
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 	mnt_drop_write_file(file);
 	return ret;
 }
@@ -2661,7 +2661,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1))
+	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags))
 		return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 
 	mutex_lock(&fs_info->volume_mutex);
@@ -2680,7 +2680,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
 	kfree(vol_args);
 out:
 	mutex_unlock(&fs_info->volume_mutex);
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 	return ret;
 }
 
@@ -2708,7 +2708,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
 	if (vol_args->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
 		return -EOPNOTSUPP;
 
-	if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
 		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 		goto out;
 	}
@@ -2721,7 +2721,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
 		ret = btrfs_rm_device(fs_info, vol_args->name, 0);
 	}
 	mutex_unlock(&fs_info->volume_mutex);
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 
 	if (!ret) {
 		if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
@@ -2752,7 +2752,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
 	if (ret)
 		return ret;
 
-	if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+	if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
 		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 		goto out_drop_write;
 	}
@@ -2772,7 +2772,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
 		btrfs_info(fs_info, "disk deleted %s", vol_args->name);
 	kfree(vol_args);
 out:
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 out_drop_write:
 	mnt_drop_write_file(file);
 
@@ -4442,13 +4442,11 @@ static long btrfs_ioctl_dev_replace(struct btrfs_fs_info *fs_info,
 			ret = -EROFS;
 			goto out;
 		}
-		if (atomic_xchg(
-			&fs_info->mutually_exclusive_operation_running, 1)) {
+		if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
 			ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 		} else {
 			ret = btrfs_dev_replace_by_ioctl(fs_info, p);
-			atomic_set(
-			 &fs_info->mutually_exclusive_operation_running, 0);
+			clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 		}
 		break;
 	case BTRFS_IOCTL_DEV_REPLACE_CMD_STATUS:
@@ -4643,7 +4641,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 		return ret;
 
 again:
-	if (!atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+	if (!test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
 		mutex_lock(&fs_info->volume_mutex);
 		mutex_lock(&fs_info->balance_mutex);
 		need_unlock = true;
@@ -4689,7 +4687,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	}
 
 locked:
-	BUG_ON(!atomic_read(&fs_info->mutually_exclusive_operation_running));
+	BUG_ON(!test_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
 
 	if (arg) {
 		bargs = memdup_user(arg, sizeof(*bargs));
@@ -4745,11 +4743,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 
 do_balance:
 	/*
-	 * Ownership of bctl and mutually_exclusive_operation_running
+	 * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP
 	 * goes to to btrfs_balance.  bctl is freed in __cancel_balance,
 	 * or, if restriper was paused all the way until unmount, in
-	 * free_fs_info.  mutually_exclusive_operation_running is
-	 * cleared in __cancel_balance.
+	 * free_fs_info.  The flag is cleared in __cancel_balance.
 	 */
 	need_unlock = false;
 
@@ -4769,7 +4766,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 	mutex_unlock(&fs_info->balance_mutex);
 	mutex_unlock(&fs_info->volume_mutex);
 	if (need_unlock)
-		atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+		clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 out:
 	mnt_drop_write_file(file);
 	return ret;

fs/btrfs/volumes.c

@@ -3761,7 +3761,7 @@ static void __cancel_balance(struct btrfs_fs_info *fs_info)
 	if (ret)
 		btrfs_handle_fs_error(fs_info, ret, NULL);
 
-	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 }
 
 /* Non-zero return value signifies invalidity */
@@ -3941,7 +3941,7 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
 		__cancel_balance(fs_info);
 	else {
 		kfree(bctl);
-		atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+		clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 	}
 	return ret;
 }
@@ -4031,7 +4031,7 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
 	btrfs_balance_sys(leaf, item, &disk_bargs);
 	btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);
 
-	WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
+	WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
 
 	mutex_lock(&fs_info->volume_mutex);
 	mutex_lock(&fs_info->balance_mutex);