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Message-ID: <1bcf7d5e-b89c-4118-b872-c8896bdbdc19@paulmck-laptop> Date: Thu, 8 May 2025 16:32:39 -0700 From: "Paul E. McKenney" <paulmck@...nel.org> To: linux-kernel@...r.kernel.org Cc: Andrew Morton <akpm@...ux-foundation.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, Mateusz Guzik <mjguzik@...il.com>, Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, John Ogness <john.ogness@...utronix.de>, Sergey Senozhatsky <senozhatsky@...omium.org>, Jon Pan-Doh <pandoh@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, Karolina Stolarek <karolina.stolarek@...cle.com> Subject: [PATCH v5 0/21] ratelimit: Reduce ratelimit's false-positive misses Hello! This v5 series replaces open-coded uses of the ratelimit_state structure with formal APIs, counts all rate-limit misses, replaces jiffies=0 special case with a flag, provides a ___ratelimit() trylock-failure fastpath to (almost) eliminate false-positive misses, simplifies the code, and adds a simple "smoke" test along with a simple stress test. The key point of this series is the reduction of false-positive misses. More could be done to avoid open-coded access to the ->interval and ->burst fields, and to tighten up checking of user input for these fields, but those are jobs for later patches. The individual patches are as follows: 1. Create functions to handle ratelimit_state internals. 2. Avoid open-coded use of ratelimit_state structure's ->missed field. 3. Avoid open-coded use of ratelimit_state structure's ->missed field. 4. Avoid open-coded use of ratelimit_state structure's internals. 5. Convert the ->missed field to atomic_t. 6. Count misses due to lock contention. 7. Avoid jiffies=0 special case. 8. Reduce ___ratelimit() false-positive rate limiting, courtesy of Petr Mladek. 9. Allow zero ->burst to disable ratelimiting. 10. Force re-initialization when rate-limiting re-enabled. 11. Don't flush misses counter if RATELIMIT_MSG_ON_RELEASE. 12. Avoid atomic decrement if already rate-limited. 13. Avoid atomic decrement under lock if already rate-limited. 14. Warn if ->interval or ->burst are negative, courtesy of Petr Mladek. 15. Simplify common-case exit path. 16. Use nolock_ret label to save a couple of lines of code. 17. Use nolock_ret label to collapse lock-failure code. 18. Use nolock_ret restructuring to collapse common case code. 19. Drop redundant accesses to burst. 20. Add trivial kunit test for ratelimit. 21. Add stress test for ratelimit. Changes since v4: o Add a simple stress test. o Move the tests to the end of the series for bisectability. o Add Reviewed-by tags. Changes since v3: o Correctly handle zero-initialized ratelimit_state structures, being careful to avoid acquiring the uninitialized ->lock. o Remove redundant checks of the "burst" local variable. o Add Reviewed-by tags. Changes since v2: o Apply feedback from Bert Karwatzki, Srikanth Aithal, and Mark Brown, fixing a hang that happened on some systems. o Applied Reviewed-by tags and added links. o Added a prototype patch from Petr Mladek that splats if either interval or burst are negative. o Added several commits that simplify the code. Changes since v1 (RFC): o Switch from lockless fastpath to carrying out needed updates upon trylock failure, per Petr Mladek feedback. This greatly simplifies the code and is a much smaller change from the current code. There is a small performance penalty compared to the lockless fastpath, but not enough to matter. o Never unconditionally acquire the lock, again per Petr Mladek feedback. o Better define effects of non-positive burst values (always ratelimit) and non-positive interval values (never ratelimit when the burst value is positive). o The changes from Petr's original are supplied as five incremental patches, but could easily be folded into Petr's original if desired. (Left to my lazy self, they stay as-is.) Thanx, Paul ------------------------------------------------------------------------ b/drivers/char/random.c | 9 + b/drivers/gpu/drm/amd/pm/amdgpu_pm.c | 11 -- b/drivers/gpu/drm/i915/i915_perf.c | 8 - b/include/linux/ratelimit.h | 40 +++++++- b/include/linux/ratelimit_types.h | 2 b/lib/Kconfig.debug | 11 ++ b/lib/ratelimit.c | 8 - b/lib/tests/Makefile | 1 b/lib/tests/test_ratelimit.c | 79 ++++++++++++++++ include/linux/ratelimit.h | 13 +- include/linux/ratelimit_types.h | 3 lib/ratelimit.c | 165 ++++++++++++++++++++--------------- lib/tests/test_ratelimit.c | 69 ++++++++++++++ 13 files changed, 313 insertions(+), 106 deletions(-)
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