RFC Fix storing in XArray check_split tests
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- v3 RFC Latest2 patches 5 repliesIn review
- v2 RFC0 of 2 patches 0 repliesSuperseded
- v1 RFC2 patches 0 repliesSuperseded
Patches in v3 No applies recorded yet
| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/2 | XArray tests: Fix check_split tests to store correctlylib/ | +16 | 0 replies | |
| 2/2 | XArray tests: Verify xa_erase behavior in check_splitlib/ | +8 | 0 replies |
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Cover letter [RFC PATCH v3 0/2] Fix storing in XArray check_split tests
Hi,
I hit an assertion while making some modifications to lib/test_xarray.c [1] and I believe this is the fix.
In check_split, the tests split the XArray node and then store values after the split to verify that splitting worked. While storing and retrieval works as expected, the node's metadata, specifically node->nr_values, is not updated correctly.
This led to the assertion being hit in [1], since the storing process did not increment node->nr_values sufficiently, while the erasing process assumed the fully-incremented node->nr_values state.
Would like to check my understanding on these:
1. In the multi-index xarray world, is node->nr_values definitely the total number of values *and siblings* in the node?
2. IIUC xas_store() has significantly different behavior when entry is NULL vs non-NULL: when entry is NULL, xas_store() does not make assumptions on the number of siblings and erases all the way till the next non-sibling entry. This sounds fair to me, but it's also kind of surprising that it is differently handled when entry is non-NULL, where xas_store() respects xas->xa_sibs.
3. If xas_store() is dependent on its caller to set up xas correctly (also sounds fair), then there are places where xas_store() is used, like replace_page_cache_folio() or migrate_huge_page_move_mapping(), where xas is set up assuming 0 order pages. Are those buggy?
Previous versions:
+ RFC v3: Cleaned up commits and subject references (sorry for the noise!)
+ RFC v2: Rebased on Linux 7.0-rc1 (https://lore.kernel.org/all/[email protected]/T/)
+ RFC v1: https://lore.kernel.org/all/720e32d8e185d5c82659bbdede05e87b3318c413.1769818406.git.ackerleytng@google.com/
[1] https://lore.kernel.org/all/[email protected]/
Ackerley Tng (2):
XArray tests: Fix check_split tests to store correctly XArray tests: Verify xa_erase behavior in check_split
lib/test_xarray.c | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-)
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f --
2.53.0.345.g96ddfc5eaa-goog