fix #27211210

commit 508c8772760d4ef9c1a044519b564710c3684fc5 upstream.

we need to reload ->d_flags after the call of ->d_manage() - the thing
might've been called with dentry still negative and have the damn thing
turned positive while we'd waited.

Fixes: d41efb522e90 "fs/namei.c: pull positivity check into follow_managed()"
Reported-by: NIan Kent <raven@themaw.net>
Tested-by: NIan Kent <raven@themaw.net>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: NJoseph Qi <joseph.qi@linux.alibaba.com>