lib/tests: add KUnit tests for errseq

2026-09-06T03:23:24+00:00

The errseq_t infrastructure (lib/errseq.c) underpins writeback error reporting but has no regression tests. Its semantics are subtle enough to have needed fixing before: commit b4678df184b3 ("errseq: Always report a writeback error once") changed how unseen errors reach new samplers. Add a KUnit suite covering the documented single-threaded semantics: - a zeroed errseq_t is the "no error yet" epoch - errors are recorded, overwrite one another, and both ends of the valid errno range round-trip exactly - an error nobody has seen samples as zero, so a check against a fresh sample still reports it - errseq_check_and_advance() reports a given error exactly once per cursor and leaves the cursor in place when nothing has changed - once an error has been seen, a fresh sample is current and a check against it reports nothing - the same error recorded again after being seen is reported again, even to a cursor that consumed the first occurrence while another cursor marked the repeat as seen - independent cursors each observe each error The lockless behaviour of errseq_t under concurrent updates and the WARN path for invalid error values are deliberately out of scope. Tested with ./tools/testing/kunit/kunit.py run, with a kunitconfig enabling CONFIG_KUNIT=y and CONFIG_ERRSEQ_KUNIT_TEST=y; all 13 tests pass under ARCH=um. Link: https://lore.kernel.org/20260812-errseq-kunit-v1-1-312be4c3aa0d@gmail.com Signed-off-by: Thomas Maarseveen Acked-by: Jeff Layton Cc: David Gow Signed-off-by: Andrew Morton

kernel/git/next/linux-next.git/lib/tests/errseq_kunit.c, branch master

lib/tests: add KUnit tests for errseq