xfsprogs/xfsprogs-5.19.0-xfs-fix-off-by-one-error-in-xfs_btree_space_to_heigh.patch
Pavel Reichl 17fdafd9b5 New upstream release 5.19.0
Upstream now has these patches:
	c1c71781 mkfs: update manpage of bigtime and inobtcount
	1c08f0ae mkfs: enable inobtcount and bigtime by default

* So do not amend the man page and do not change the default option
	values for inobtcount and bigtime.
* But continue turning off inobtcount and bigtime for kernels older
	than 5.10

Unlike upstream RHEL-9 will continue to support tiny filesystems,
but add warning about deprecation.

Backport all "Fixing" patches relevant to 5.19

Resolves: rhbz#2142910
Signed-off-by: Pavel Reichl <preichl@redhat.com>
2023-04-14 21:51:06 +02:00

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Diff

From a68dabd45f3591456ecf7e35f6a6077db79f6bc6 Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <djwong@kernel.org>
Date: Wed, 15 Mar 2023 15:59:35 +0100
Subject: [PATCH] xfs: fix off-by-one error in xfs_btree_space_to_height
Source kernel commit: c0f399ff51495ac8d30367418f4f6292ecd61fbe
Lately I've been stress-testing extreme-sized rmap btrees by using the
(new) xfs_db bmap_inflate command to clone bmbt mappings billions of
times and then using xfs_repair to build new rmap and refcount btrees.
This of course is /much/ faster than actually FICLONEing a file billions
of times.
Unfortunately, xfs_repair fails in xfs_btree_bload_compute_geometry with
EOVERFLOW, which indicates that xfs_mount.m_rmap_maxlevels is not
sufficiently large for the test scenario. For a 1TB filesystem (~67
million AG blocks, 4 AGs) the btheight command reports:
$ xfs_db -c 'btheight -n 4400801200 -w min rmapbt' /dev/sda
rmapbt: worst case per 4096-byte block: 84 records (leaf) / 45 keyptrs (node)
level 0: 4400801200 records, 52390491 blocks
level 1: 52390491 records, 1164234 blocks
level 2: 1164234 records, 25872 blocks
level 3: 25872 records, 575 blocks
level 4: 575 records, 13 blocks
level 5: 13 records, 1 block
6 levels, 53581186 blocks total
The AG is sufficiently large to build this rmap btree. Unfortunately,
m_rmap_maxlevels is 5. Augmenting the loop in the space->height
function to report height, node blocks, and blocks remaining produces
this:
ht 1 node_blocks 45 blockleft 67108863
ht 2 node_blocks 2025 blockleft 67108818
ht 3 node_blocks 91125 blockleft 67106793
ht 4 node_blocks 4100625 blockleft 67015668
final height: 5
The goal of this function is to compute the maximum height btree that
can be stored in the given number of ondisk fsblocks. Starting with the
top level of the tree, each iteration through the loop adds the fanout
factor of the next level down until we run out of blocks. IOWs, maximum
height is achieved by using the smallest fanout factor that can apply
to that level.
However, the loop setup is not correct. Top level btree blocks are
allowed to contain fewer than minrecs items, so the computation is
incorrect because the first time through the loop it should be using a
fanout factor of 2. With this corrected, the above becomes:
ht 1 node_blocks 2 blockleft 67108863
ht 2 node_blocks 90 blockleft 67108861
ht 3 node_blocks 4050 blockleft 67108771
ht 4 node_blocks 182250 blockleft 67104721
ht 5 node_blocks 8201250 blockleft 66922471
final height: 6
Fixes: 9ec691205e7d ("xfs: compute the maximum height of the rmap btree when reflink enabled")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Pavel Reichl <preichl@redhat.com>
---
libxfs/xfs_btree.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/libxfs/xfs_btree.c b/libxfs/xfs_btree.c
index 65d38637..38a3092d 100644
--- a/libxfs/xfs_btree.c
+++ b/libxfs/xfs_btree.c
@@ -4663,7 +4663,12 @@ xfs_btree_space_to_height(
const unsigned int *limits,
unsigned long long leaf_blocks)
{
- unsigned long long node_blocks = limits[1];
+ /*
+ * The root btree block can have fewer than minrecs pointers in it
+ * because the tree might not be big enough to require that amount of
+ * fanout. Hence it has a minimum size of 2 pointers, not limits[1].
+ */
+ unsigned long long node_blocks = 2;
unsigned long long blocks_left = leaf_blocks - 1;
unsigned int height = 1;
--
2.40.0