Claude review: kunit: Add support for suppressing warning backtraces

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Overall Series Review

Subject: kunit: Add support for suppressing warning backtraces
Author: Albert Esteve <aesteve@redhat.com>
Patches: 20
Reviewed: 2026-04-23T09:52:25.890322

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This v7 series adds KUnit infrastructure for suppressing WARN() backtraces during tests that intentionally trigger them. The approach is sound: hooks are placed at two points in the warning path (`warn_slowpath_fmt()` for non-`__WARN_FLAGS` architectures, and `__report_bug()` for `__WARN_FLAGS` architectures), with an RCU-protected per-task suppression list. The design avoids touching `include/asm-generic/bug.h` and requires no architecture-specific code.

The series is well-structured, has good test coverage, and addresses a real problem (noisy backtraces in CI from tests that intentionally pass bad parameters).

**One significant correctness issue**: The RCU-protected `suppressed_warnings` list has no write-side lock. `list_add_rcu()` and `list_del_rcu()` are called without any mutual exclusion, which is incorrect per the RCU list API contract. While KUnit tests typically run sequentially, this is a latent data corruption bug if tests ever run concurrently.

There is also a minor ordering issue in patch 2 where the atomic counter is incremented before `list_add_rcu()`, creating a window where `__kunit_is_suppressed_warning()` enters the RCU list traversal but doesn't find the entry yet. This is benign (returns false instead of true), but worth noting.

Overall: good concept, near-mergeable, needs the write-side lock fix.

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