mbcache: Don't reclaim used entries

hulk inclusion
category: bugfix
bugzilla: 186975, https://gitee.com/openeuler/kernel/issues/I5HT6F
CVE: NA

Reference: https://patchwork.ozlabs.org/project/linux-ext4/list/?series=309169



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Do not reclaim entries that are currently used by somebody from a
shrinker. Firstly, these entries are likely useful. Secondly, we will
need to keep such entries to protect pending increment of xattr block
refcount.

CC: stable@vger.kernel.org
Fixes: 82939d79 ("ext4: convert to mbcache2")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>