mainline inclusion
from md-next
commit ddc489e066cd267b383c0eed4f576f6bdb154588
category: performance
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5PRMO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/song/md.git/commit/?h=md-next&id=ddc489e066cd267b383c0eed4f576f6bdb154588

---------------------

Currently, wait_barrier() will hold 'resync_lock' to read 'conf->barrier',
and io can't be dispatched until 'barrier' is dropped.

Since holding the 'barrier' is not common, convert 'resync_lock' to use
seqlock so that holding lock can be avoided in fast path.
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-and-tested-by: NLogan Gunthorpe <logang@deltatee.com>
Signed-off-by: NSong Liu <song@kernel.org>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>