[PATCH 1/2] btrfs: do not commit transaction after adding one device

[Qu Wenruo <wqu@suse.com>]

[BUG]
There is at least one report that btrfs falls to deadly ENOSPC
situation, where without adding new space btrfs would fail to commit any
transaction due to ENOSPC.

However this last resort device adding would not work if the filesystem
is using multi-device metadata profiles (RAID1*, RAID0, RAID5/6), as
after each device added, btrfs would commit the transaction, falling
back to read-only due to ENOSPC.

[CAUSE]
Of course we should not fail a transaction due to ENOSPC in the first
place, as this means at metadata reservation stage we did wrong
calculation.

But the current behavior of device add is also a little too strict,
considering device adding is the last-resort for ENOSPC, we should at
least allow end users to determine if they want to commit transaction or
not.

[FIX]
Instead of committing transaction, just end the current one.

Whether the fs would be synced would be determined at user space
(normally by btrfs-progs) instead.

Link: https://lore.kernel.org/linux-btrfs/CA+W5K0r4Lv4fPf+mWWf-ppgsjyz+wOKdBRgBR6UnQafwL7HPtg@mail.gmail.com/
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/volumes.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 70d69d4b44d2..eda90d1c881f 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2789,7 +2789,8 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 		btrfs_sysfs_update_sprout_fsid(fs_devices);
 	}
 
-	ret = btrfs_commit_transaction(trans);
+	ret = btrfs_end_transaction(trans);
+	trans = NULL;
 
 	if (seeding_dev) {
 		mutex_unlock(&uuid_mutex);
@@ -2803,15 +2804,6 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 		if (ret < 0)
 			btrfs_handle_fs_error(fs_info, ret,
 				    "Failed to relocate sys chunks after device initialization. This can be fixed using the \"btrfs balance\" command.");
-		trans = btrfs_attach_transaction(root);
-		if (IS_ERR(trans)) {
-			if (PTR_ERR(trans) == -ENOENT)
-				return 0;
-			ret = PTR_ERR(trans);
-			trans = NULL;
-			goto error_sysfs;
-		}
-		ret = btrfs_commit_transaction(trans);
 	}
 
 	/*
-- 
2.41.0