xfs: longest free extent no need consider postalloc

hulk inclusion
category: bugfix
bugzilla: 188788, https://gitee.com/openeuler/kernel/issues/I76JSK


CVE: NA

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

xfs_alloc_space_available need to make sure the longest free extent
can satisfy extra blocks needed for agfl fixup and also the really
needed block for the latter allocation. Or the latter agfl filling may
consume some blocks within the longest free extent, which can lead to
that all the free extent can not satisfy the really block allocation.

The arg 'min_free' show that actually blocks we need fill agfl up to.
But after commit aa1ab9a77d89 ("xfs: fix xfs shutdown since we reserve
more blocks in agfl fixup"), the 'min_free' will add the reserve blocks
for second fixup, but leave agfl blocks does not include this.

Actually, what we want was just reserve more blocks to satisfy second
fixup, we will not fill agfl with that so many blocks, so the args for
xfs_alloc_longest_free_extent should not consider postalloc. And fix
agflcount in xfs_alloc_space_available too.

Fixes: aa1ab9a77d89 ("xfs: fix xfs shutdown since we reserve more blocks in agfl fixup")
Signed-off-by: yangerkun <yangerkun@huawei.com>
Signed-off-by: Long Li <leo.lilong@huawei.com>