From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794262781; b=j8b+iuKaMtSapxFMHyKTuqIay7fm7BjLGJzs510eW45AkxPNtRL0SS32ZcEnGrA8Q56T 6q+TII2jBg7bez/QfLQJrN+e5M5M7cEVmAS92aOQTugUNAerSvD026Cicz5RpBgF3k1DK ljlhzql5eYqW/wVvJHrFBkRNn6AuWJLtmQxq3Kmjyvfg/tQAYbDlzOxEQ0NSaz9frKp9y TKMdZ29jPv77FmmGn04TgUvbAC/Mh3VPEkxH3bX6a/fGg0vAtdt8qXFPqvUkqWgj5pXHx HYjigMptvmGf/88D3Pp2qPEdeOpepMEYxN0lXl7sdxQOQeSYzh0sffwAsAnK0t7OowQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794262781; h=Received:DKIM-Signature:Received:From:To:Cc:Subject:Date:Message-Id: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=OryNfxwVsVz5lbqPtFhffPyHOBTyKVHtLCZv06UqWZY=; b=mILDib+4k/a8uCaLwTtLkx//Zng8WWp48tnB/RfiuqdwYvFRliKKGMb1pExAHJPGA+aK LAW8RmkjzpKWC/gbVMN9gnEQejgXDnXuhU3Y6cJe0M0DlbfyZfzI+3YRLtb0f+3IRDPnb MiuP6OdsFtsE+j+ifvmgCJXd6bXPxK5tsmBv9YZ9yWd/slz5Xl9xdiI25cJ539vXu1kpB ae903y/YtXcBnToi0VxmEcY07fTg4L45vKDXJ8NrzUbt97CFRagZpFePPucQE9P90m0yZ XVuxfe0WGOoa96Bcng5LaQOA0I+i85iWOnEen3cFEbLSvkwJsWOU30YsCefZtfjhcmQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=DF3w5oPE; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 179CC606A331; Mon, 9 Nov 2026 22:19:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=DF3w5oPE Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4C041F008A4; Mon, 9 Nov 2026 22:19:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794262780; bh=OryNfxwVsVz5lbqPtFhffPyHOBTyKVHtLCZv06UqWZY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DF3w5oPEb9wrpwdMpIrI9KZt6v1J0RxTFT/kxTzRqsSEIdWBTwpwZkZkHp4Le9Kcu HtT25trnEDHhBX4gBXfAVow1YPm0NRrG2RCdj5JOC+CevaSr+iDlsulXO1RGvi0iGE szCgQof1g3R1saJOyxahE+Pg0TJYXljXUFFD/jeT9ESDgJz3C0GCvFhoWbLEas4vcP WenuFeFE+jPtev0xVRtVnoqTu8k/CUimF6Briy/GcaPuV5pk3Q3AS8UIizsqFDUMAe 9w2L/K/kPlbVO1xtWabLt8kLLQnXu7aszUstWgHDf7lzqsEEDV0b6+gFvsWen0551Y eUUIfkOpMZEMg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id AB92ACE0CC1; Mon, 9 Nov 2026 14:19:40 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" , Andrew Morton Subject: [PATCH 1/8] rcutorture: Enable RCU_BOOST where supported Date: Mon, 9 Nov 2026 14:19:32 -0800 Message-Id: <20261109221939.2070171-1-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Currently, RCU_BOOST depends on RCU_EXPERT, and is therefore often disabled in stress-test such as those run by syzbot. This means that if syzbot runs a test that overloads CPUs on kernels built with PREEMPT_RCU, RCU CPU stall warnings are not unexpected. What happens is that a low-priority task in an RCU read-side critical section is preempted, cannot be priority boosted, and stays that way for more than 21 seconds. This commit therefore drops RCU_EXPERT from the RCU_BOOST "depends on" line and removes the prompt, thus directly driving RCU_BOOST from the kernel configuration so as to enable it anywhere it is supported and might help. This commit is also marked experimental because neither Ubuntu, Fedora, nor CentOS enable RCU_BOOST. This suggests less testing of RCU priority boosting than one might wish. Reported-by: Andrew Morton Closes: https://lore.kernel.org/all/20260805122952.6ae38af69a0457779cb44359@linux-foundation.org/ Signed-off-by: Paul E. McKenney --- kernel/rcu/Kconfig | 10 ++++------ tools/testing/selftests/rcutorture/configs/rcu/NOCB01 | 1 - tools/testing/selftests/rcutorture/configs/rcu/NOCB02 | 1 - tools/testing/selftests/rcutorture/configs/rcu/TREE01 | 1 - tools/testing/selftests/rcutorture/configs/rcu/TREE02 | 1 - tools/testing/selftests/rcutorture/configs/rcu/TREE08 | 1 - .../testing/selftests/rcutorture/configs/rcuscale/TINY | 1 - .../selftests/rcutorture/configs/rcuscale/TRACE01 | 1 - .../testing/selftests/rcutorture/configs/rcuscale/TREE | 1 - .../selftests/rcutorture/configs/rcuscale/TREE54 | 1 - .../selftests/rcutorture/configs/refscale/NOPREEMPT | 1 - .../selftests/rcutorture/configs/refscale/PREEMPT | 1 - .../testing/selftests/rcutorture/configs/refscale/TINY | 1 - 13 files changed, 4 insertions(+), 18 deletions(-) diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index bc9483c0b5d84..7b605fa1f576e 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -237,17 +237,15 @@ config RCU_FANOUT_LEAF Take the default if unsure. config RCU_BOOST - bool "Enable RCU priority boosting" - depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT - default y if PREEMPT_RT + bool + default y if (RT_MUTEXES && PREEMPT_RCU) || PREEMPT_RT help This option boosts the priority of preempted RCU readers that block the current preemptible RCU grace period for too long. This option also prevents heavy loads from blocking RCU - callback invocation. + callback invocation. It is now automatically enabled in + any kernel that can benefit from it and that can support it. - Say Y here if you are working with real-time apps or heavy loads - Say N here if you are unsure. config RCU_BOOST_DELAY int "Milliseconds to delay boosting after RCU grace-period start" diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 index bbe6d28210ab5..91ca7e8b5725f 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 +++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 @@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2 CONFIG_RCU_NOCB_CPU=y CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_EQS_DEBUG=y diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 index 4c2b8cd6d8fdb..ed3f3f7b29e73 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 +++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 @@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2 CONFIG_RCU_NOCB_CPU=y CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_EQS_DEBUG=y diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE01 b/tools/testing/selftests/rcutorture/configs/rcu/TREE01 index 54b1600c7eb5f..be5bf69a1b60f 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE01 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE01 @@ -10,6 +10,5 @@ CONFIG_RCU_TRACE=y CONFIG_HOTPLUG_CPU=y CONFIG_RCU_NOCB_CPU=y CONFIG_DEBUG_LOCK_ALLOC=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE02 b/tools/testing/selftests/rcutorture/configs/rcu/TREE02 index 2871ee599891d..36b9228ae7032 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE02 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE02 @@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT_LEAF=3 CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_RCU_EXPERT=y CONFIG_DEBUG_OBJECTS=y CONFIG_DEBUG_OBJECTS_RCU_HEAD=y diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE08 b/tools/testing/selftests/rcutorture/configs/rcu/TREE08 index 8b561355b9ef2..ad7d7f873e1eb 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE08 +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE08 @@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT_LEAF=2 CONFIG_RCU_NOCB_CPU=y CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_EQS_DEBUG=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TINY b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY index c1a7d38823fba..f611b69f11895 100644 --- a/tools/testing/selftests/rcutorture/configs/rcuscale/TINY +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY @@ -11,7 +11,6 @@ CONFIG_NO_HZ_FULL=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_TRACE=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 index f3f1368b83869..69f5764159df0 100644 --- a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 @@ -11,7 +11,6 @@ CONFIG_NO_HZ_FULL=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_TRACE=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE index b10706fd03a45..5122cf08d5db2 100644 --- a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE @@ -12,7 +12,6 @@ CONFIG_HIBERNATION=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_TRACE=y diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54 b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54 index 9f83e53727969..08d30edb3b99c 100644 --- a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54 +++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54 @@ -15,7 +15,6 @@ CONFIG_RCU_FANOUT_LEAF=2 CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_RCU_TRACE=y diff --git a/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT b/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT index 1f215e17cbae2..3e7d7793acc73 100644 --- a/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT +++ b/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT @@ -14,7 +14,6 @@ CONFIG_HIBERNATION=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_KPROBES=n diff --git a/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT b/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT index 52e3ef6740567..feed29cf043f6 100644 --- a/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT +++ b/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT @@ -12,6 +12,5 @@ CONFIG_HIBERNATION=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y diff --git a/tools/testing/selftests/rcutorture/configs/refscale/TINY b/tools/testing/selftests/rcutorture/configs/refscale/TINY index 9a11b578ff344..b67ea7a9128b1 100644 --- a/tools/testing/selftests/rcutorture/configs/refscale/TINY +++ b/tools/testing/selftests/rcutorture/configs/refscale/TINY @@ -14,7 +14,6 @@ CONFIG_HIBERNATION=n CONFIG_RCU_NOCB_CPU=n CONFIG_DEBUG_LOCK_ALLOC=n CONFIG_PROVE_LOCKING=n -CONFIG_RCU_BOOST=n CONFIG_DEBUG_OBJECTS_RCU_HEAD=n CONFIG_RCU_EXPERT=y CONFIG_KPROBES=n -- 2.40.1