md: enhance checking in md_check_recovery()
For md_check_recovery():
1) if 'MD_RECOVERY_RUNING' is not set, register new sync_thread.
2) if 'MD_RECOVERY_RUNING' is set:
a) if 'MD_RECOVERY_DONE' is not set, don't do anything, wait for
md_do_sync() to be done.
b) if 'MD_RECOVERY_DONE' is set, unregister sync_thread. Current code
expects that sync_thread is not NULL, otherwise new sync_thread will
be registered, which will corrupt the array.
Make sure md_check_recovery() won't register new sync_thread if
'MD_RECOVERY_RUNING' is still set, and a new WARN_ON_ONCE() is added for
the above corruption,
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529132037.2124527-7-yukuai1@huaweicloud.com