[PATCH v2 2/4] btrfs: mark device addition as mnt_want_write_file

[Naohiro Aota <naohiro.aota@xxxxxxx>]

btrfs_init_new_device() calls btrfs_relocate_sys_chunk() which incurs
file-system internal writing. That writing can cause a deadlock with
FS freezing like as described in like as described in commit
26559780b953 ("btrfs: zoned: mark relocation as writing").

Mark the device addition as mnt_want_write_file. This is also consistent
with the removing device ioctl counterpart.

Cc: stable@xxxxxxxxxxxxxxx # 4.9+
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
 fs/btrfs/ioctl.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 60c907b14547..a6982a1fde65 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3474,8 +3474,10 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
 	return ret;
 }
 
-static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
+static long btrfs_ioctl_add_dev(struct file *file, void __user *arg)
 {
+	struct inode *inode = file_inode(file);
+	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	struct btrfs_ioctl_vol_args *vol_args;
 	bool restore_op = false;
 	int ret;
@@ -3488,6 +3490,10 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
 		return -EINVAL;
 	}
 
+	ret = mnt_want_write_file(file);
+	if (ret)
+		return ret;
+
 	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_ADD)) {
 		if (!btrfs_exclop_start_try_lock(fs_info, BTRFS_EXCLOP_DEV_ADD))
 			return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
@@ -3520,6 +3526,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
 		btrfs_exclop_balance(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED);
 	else
 		btrfs_exclop_finish(fs_info);
+	mnt_drop_write_file(file);
 	return ret;
 }
 
@@ -5443,7 +5450,7 @@ long btrfs_ioctl(struct file *file, unsigned int
 	case BTRFS_IOC_RESIZE:
 		return btrfs_ioctl_resize(file, argp);
 	case BTRFS_IOC_ADD_DEV:
-		return btrfs_ioctl_add_dev(fs_info, argp);
+		return btrfs_ioctl_add_dev(file, argp);
 	case BTRFS_IOC_RM_DEV:
 		return btrfs_ioctl_rm_dev(file, argp);
 	case BTRFS_IOC_RM_DEV_V2:
-- 
2.35.1