xfs: don't include bnobt blocks when reserving free block pool

mainline inclusion
from mainline-v5.18-rc1
commit c8c56825
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c8c568259772751a14e969b7230990508de73d9d

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

xfs_reserve_blocks controls the size of the user-visible free space
reserve pool.  Given the difference between the current and requested
pool sizes, it will try to reserve free space from fdblocks.  However,
the amount requested from fdblocks is also constrained by the amount of
space that we think xfs_mod_fdblocks will give us.  If we forget to
subtract m_allocbt_blks before calling xfs_mod_fdblocks, it will will
return ENOSPC and we'll hang the kernel at mount due to the infinite
loop.

In commit fd43cf60, we decided that xfs_mod_fdblocks should not hand
out the "free space" used by the free space btrees, because some portion
of the free space btrees hold in reserve space for future btree
expansion.  Unfortunately, xfs_reserve_blocks' estimation of the number
of blocks that it could request from xfs_mod_fdblocks was not updated to
include m_allocbt_blks, so if space is extremely low, the caller hangs.

Fix this by creating a function to estimate the number of blocks that
can be reserved from fdblocks, which needs to exclude the set-aside and
m_allocbt_blks.

Found by running xfs/306 (which formats a single-AG 20MB filesystem)
with an fstests configuration that specifies a 1k blocksize and a
specially crafted log size that will consume 7/8 of the space (17920
blocks, specifically) in that AG.

Cc: Brian Foster <bfoster@redhat.com>
Fixes: fd43cf60 ("xfs: set aside allocation btree blocks from block reservation")
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Conflicts:
	fs/xfs/xfs_mount.h
	[ 15f04fdc("xfs: remove infinite loop when reserving
	  free block pool") applied earlier. ]
Signed-off-by: NZhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

fs/xfs/xfs_mount.c

@@ -1295,7 +1295,7 @@ xfs_mod_fdblocks(
 	 * problems (i.e. transaction abort, pagecache discards, etc.) than
 	 * slightly premature -ENOSPC.
 	 */
-	set_aside = mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
+	set_aside = xfs_fdblocks_unavailable(mp);
 	percpu_counter_add_batch(&mp->m_fdblocks, delta, batch);
 	if (__percpu_counter_compare(&mp->m_fdblocks, set_aside,
 				     XFS_FDBLOCKS_BATCH) >= 0) {

fs/xfs/xfs_mount.h

@@ -478,7 +478,7 @@ static inline uint64_t
 xfs_fdblocks_unavailable(
 	struct xfs_mount	*mp)
 {
-	return mp->m_alloc_set_aside;
+	return mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
 }
 
 extern int	xfs_mod_fdblocks(struct xfs_mount *mp, int64_t delta,