commit 08530d6e63 upstream.
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 6ed05643dd ("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: 6ed05643dd ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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