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Fixed issue where ckfetches hid cached btree nodes from ckmeta

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In lfsr_mtree_traverse, we were explicitly not checking btree nodes when
ckfetches was enabled. This was an attempt to avoid double-checking btree
nodes when using both ckfetches and ckmeta.

Unfortunately this misses errors introduced _after_ fetch in btrees we
keep around in RAM. We still want to find these when doing an explicit
ckmeta scan!

---

Removing this special case _does_ mean we will be back to redundantly
checking non-cached btree nodes, but I think this is a case of better
safe than sorry.

In the future we may cache btree nodes more aggressively depending on
available RAM, and it would be a shame if that accidentally leads to a
weaker filesystem.

Worst case we can always revisit this ckfetches/ckmeta double-fetching
in the future if it become a bottleneck.

Found by our test_ck_spam_fwrite_fuzz test.

This actually saves a tiny bit of code, but at the cost of redundantly
checking non-cached btree nodes:

                     code          stack          ctx
  default before:   38512           2624          640
  default after:    38512 (+0.0%)   2624 (+0.0%)  640 (+0.0%)

  ckfetches before: 38766           2656          640
  ckfetches after:  38762 (-0.0%)   2656 (+0.0%)  640 (+0.0%)
This commit is contained in:
Christopher Haster
2025-01-21 16:47:20 -06:00
parent f90906458a
commit ab26437e46
1 changed files with 5 additions and 5 deletions
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lfs.c
+5 -5
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@@ -9541,13 +9541,13 @@ static int lfsr_mtree_traverse(lfs_t *lfs, lfsr_traversal_t *t,
}
// validate btree nodes?
//
// this may end up revalidating some btree nodes when ckfetches is
// enabled, but we need to revalidate cached btree nodes or we risk
// missing errors in ckmeta scans
if ((lfsr_t_isckmeta(t->o.o.flags)
|| lfsr_t_isckdata(t->o.o.flags))
&& tag == LFSR_TAG_BRANCH
// note ckfetches already validates btree nodes
&& LFS_IFDEF_CKFETCHES(
!lfsr_m_isckfetches(lfs->flags),
true)) {
&& tag == LFSR_TAG_BRANCH) {
lfsr_rbyd_t *rbyd = (lfsr_rbyd_t*)bptr.data.u.buffer;
err = lfsr_rbyd_fetchck(lfs, rbyd,
rbyd->blocks[0], rbyd->trunk,