From nobody Mon Feb 9 16:18:15 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 30DC717C77 for ; Wed, 30 Apr 2025 01:05:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745975127; cv=none; b=ciZpi67MpnCu87m4Iu5X9ZYo4k3wskWp9vVuvripItmTtpsoi3hPK2D+l57ZhSWyc23AGow8VBejtYI9UvDe+c4remJFZ/ANfo0aNUbP82Vmhb2BY6vXo+hbolXpmaiTZepEwuyKgMJfy2UcNFn6B33TUYcaeX/qWep7+Lfn/OI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745975127; c=relaxed/simple; bh=ntY2Sw3SfTBZAtAeM3adbzynb7JDNJCcwtct5/GAXqc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Mh4UT1uOhRAsn6PXxvqEVWHrVSigBkATJR7jJtOO1EGSKdjBo/fMyMcHAUfeJPjfcbTCSHZ6pGG/WAWAFRNxl34i5n69q/cfl6F7wcm6B3RATNIInt3LkiW7xhz25WA24SAvpC3gMPl3g8Rc6q2ClK2zTAjIjCc4q0kzMdcQhUo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XkBGKBlH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XkBGKBlH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02D77C4CEED; Wed, 30 Apr 2025 01:05:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745975127; bh=ntY2Sw3SfTBZAtAeM3adbzynb7JDNJCcwtct5/GAXqc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XkBGKBlHwR6pN+H09J8wazqbf5d+JPrS/+9xwhoAAvpL7nY7xPDmZSwD28eiNsgGi aadFusgQHmZuMX1yIi42v+zzoQilitGoSSoxak6lAmWGl1be31uD8TUE5h9ZPKrzF1 ql/55/fWyncn9PvLD7kCHKFOxL1If4u+feMaFqelxzQlCIuoPTDyMCa87qIuhXrun6 0zIJyhPaZgcFGGC26NnsqtwkThJJBtHnni0kaJfNHM8ZlZBrM4QnGd6nn4bBrvdd7M J4KPuC1g1R3Giw9f8nke84tIS1nNUAvyJs/MwKFldYU/MHcGcIq1mVJym9v+Ni1tww d5y2zlvfAd07Q== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 93526CE0F53; Tue, 29 Apr 2025 18:05:25 -0700 (PDT) From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, Andrew Morton , Kuniyuki Iwashima , Mateusz Guzik , Petr Mladek , Steven Rostedt , John Ogness , Sergey Senozhatsky , Jon Pan-Doh , Bjorn Helgaas , Karolina Stolarek , "Paul E . McKenney" Subject: [PATCH v4 09/20] ratelimit: Reduce ___ratelimit() false-positive rate limiting Date: Tue, 29 Apr 2025 18:05:13 -0700 Message-Id: <20250430010524.3614408-9-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Petr Mladek Retain the locked design, but check rate-limiting even when the lock could not be acquired. Link: https://lore.kernel.org/all/Z_VRo63o2UsVoxLG@pathway.suse.cz/ Link: https://lore.kernel.org/all/fbe93a52-365e-47fe-93a4-44a44547d601@paul= mck-laptop/ Link: https://lore.kernel.org/all/20250423115409.3425-1-spasswolf@web.de/ Signed-off-by: Petr Mladek Signed-off-by: Paul E. McKenney Cc: Petr Mladek Cc: Andrew Morton Cc: Kuniyuki Iwashima Cc: Mateusz Guzik Cc: Steven Rostedt Cc: John Ogness Cc: Sergey Senozhatsky --- include/linux/ratelimit.h | 2 +- include/linux/ratelimit_types.h | 2 +- lib/ratelimit.c | 51 ++++++++++++++++++++++++--------- 3 files changed, 40 insertions(+), 15 deletions(-) diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h index adfec24061d16..7aaad158ee373 100644 --- a/include/linux/ratelimit.h +++ b/include/linux/ratelimit.h @@ -44,7 +44,7 @@ static inline void ratelimit_state_reset_interval(struct = ratelimit_state *rs, in raw_spin_lock_irqsave(&rs->lock, flags); rs->interval =3D interval_init; rs->flags &=3D ~RATELIMIT_INITIALIZED; - rs->printed =3D 0; + atomic_set(&rs->rs_n_left, rs->burst); ratelimit_state_reset_miss(rs); raw_spin_unlock_irqrestore(&rs->lock, flags); } diff --git a/include/linux/ratelimit_types.h b/include/linux/ratelimit_type= s.h index ef6711b6b229f..b19c4354540ab 100644 --- a/include/linux/ratelimit_types.h +++ b/include/linux/ratelimit_types.h @@ -18,7 +18,7 @@ struct ratelimit_state { =20 int interval; int burst; - int printed; + atomic_t rs_n_left; atomic_t missed; unsigned int flags; unsigned long begin; diff --git a/lib/ratelimit.c b/lib/ratelimit.c index bd6e3b429e333..90c9fe57eb422 100644 --- a/lib/ratelimit.c +++ b/lib/ratelimit.c @@ -39,12 +39,22 @@ int ___ratelimit(struct ratelimit_state *rs, const char= *func) return 1; =20 /* - * If we contend on this state's lock then almost - * by definition we are too busy to print a message, - * in addition to the one that will be printed by - * the entity that is holding the lock already: + * If we contend on this state's lock then just check if + * the current burst is used or not. It might cause + * false positive when we are past the interval and + * the current lock owner is just about to reset it. */ if (!raw_spin_trylock_irqsave(&rs->lock, flags)) { + unsigned int rs_flags =3D READ_ONCE(rs->flags); + + if (rs_flags & RATELIMIT_INITIALIZED && burst) { + int n_left; + + n_left =3D atomic_dec_return(&rs->rs_n_left); + if (n_left >=3D 0) + return 1; + } + ratelimit_state_inc_miss(rs); return 0; } @@ -52,27 +62,42 @@ int ___ratelimit(struct ratelimit_state *rs, const char= *func) if (!(rs->flags & RATELIMIT_INITIALIZED)) { rs->begin =3D jiffies; rs->flags |=3D RATELIMIT_INITIALIZED; + atomic_set(&rs->rs_n_left, rs->burst); } =20 if (time_is_before_jiffies(rs->begin + interval)) { - int m =3D ratelimit_state_reset_miss(rs); + int m; + + /* + * Reset rs_n_left ASAP to reduce false positives + * in parallel calls, see above. + */ + atomic_set(&rs->rs_n_left, rs->burst); + rs->begin =3D jiffies; =20 + m =3D ratelimit_state_reset_miss(rs); if (m) { if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) { printk_deferred(KERN_WARNING "%s: %d callbacks suppressed\n", func, m); } } - rs->begin =3D jiffies; - rs->printed =3D 0; } - if (burst && burst > rs->printed) { - rs->printed++; - ret =3D 1; - } else { - ratelimit_state_inc_miss(rs); - ret =3D 0; + if (burst) { + int n_left; + + /* The burst might have been taken by a parallel call. */ + n_left =3D atomic_dec_return(&rs->rs_n_left); + if (n_left >=3D 0) { + ret =3D 1; + goto unlock_ret; + } } + + ratelimit_state_inc_miss(rs); + ret =3D 0; + +unlock_ret: raw_spin_unlock_irqrestore(&rs->lock, flags); =20 return ret; --=20 2.40.1