btrfs: qgroup: fix qgroup create ioctl returning success after quotas disabled

When quotas are disabled qgroup ioctls are supposed to return -ENOTCONN,
but the qgroup create ioctl stopped doing that when it races with a quota
disable operation, returning 0 instead. This change of behaviour happened
in commit 6ed05643ddb1 ("btrfs: create qgroup earlier in snapshot
creation").

The issue happens as follows:

1) Task A enters btrfs_ioctl_qgroup_create(), qgroups are enabled and so
   qgroup_enabled() returns true since fs_info->quota_root is not NULL;

2) Task B enters btrfs_ioctl_quota_ctl() -> btrfs_quota_disable() and
   disables qgroups, so now fs_info->quota_root is NULL;

3) Task A enters btrfs_create_qgroup() and calls btrfs_qgroup_mode(),
   which returns BTRFS_QGROUP_MODE_DISABLED since quotas are disabled,
   and then btrfs_create_qgroup() returns 0 to the caller, which makes
   the ioctl return 0 instead of -ENOTCONN.

   The check for fs_info->quota_root and returning -ENOTCONN if it's NULL
   is made only after the call btrfs_qgroup_mode().

Fix this by moving the check for disabled quotas with btrfs_qgroup_mode()
into transaction.c:create_pending_snapshot(), so that we don't abort the
transaction if btrfs_create_qgroup() returns -ENOTCONN and quotas are
disabled.

Fixes: 6ed05643ddb1 ("btrfs: create qgroup earlier in snapshot creation")
CC: stable@vger.kernel.org # 6.12+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index eb1bb57dee7df5135a7b8def9d61a52f764ddf08..ae9bc7c71a347e161f6829c897714f695d76a7a0 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1662,9 +1662,6 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
        struct btrfs_qgroup *prealloc = NULL;
        int ret = 0;
 
-       if (btrfs_qgroup_mode(fs_info) == BTRFS_QGROUP_MODE_DISABLED)
-               return 0;
-
        mutex_lock(&fs_info->qgroup_ioctl_lock);
        if (!fs_info->quota_root) {
                ret = -ENOTCONN;

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 2e07c90be5cd15c3c43fea9d2b7e4cdf5089665e..c5c0d9cf1a8088ece3dc83419da02e3022e3bfc6 100644 (file)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1735,8 +1735,10 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 
        ret = btrfs_create_qgroup(trans, objectid);
        if (ret && ret != -EEXIST) {
-               btrfs_abort_transaction(trans, ret);
-               goto fail;
+               if (ret != -ENOTCONN || btrfs_qgroup_enabled(fs_info)) {
+                       btrfs_abort_transaction(trans, ret);
+                       goto fail;
+               }
        }
 
        /*