From mboxrd@z Thu Jan 1 00:00:00 1970 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 4EE8022DA14; Mon, 5 May 2025 23:05:29 +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=1746486330; cv=none; b=WS57V33dnsQ3W+p4aZZZ+P2aucMUrOPk5qBm9TF00fYxfy9lVFQJWzN455RrQl2yUrqBWCWueG13JV9J+UZLwDpyGxCdVbETpOLfnn9dZdMOmYQnltaEPESUSEVWTnzrMt5eAu84Bqxgm+jVgt9D3fMLaS+pgb+nHGHF7EifYsE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746486330; c=relaxed/simple; bh=QXzH7nV2Y+fEKkz2afxoldpnLN/Y1oQVhmH8CU9tFHQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bL/59a/1UMPPDm+jDaYYlufPPKDgZh+ME5hNPz0rGAKrpKA3QjMPVQhZQY768eOhWOmQEYuBuB0u53TlT0LPCV13kIytM9Iw5f8Z8ofuwTfQtKLJrH2Bfabpg2CaC7ObzjIsWJKiEr7lKwZupEyXU38IIe6N8b1nUrW6vZphftQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Wf0pmqYU; 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="Wf0pmqYU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C8FD2C4CEEF; Mon, 5 May 2025 23:05:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746486329; bh=QXzH7nV2Y+fEKkz2afxoldpnLN/Y1oQVhmH8CU9tFHQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Wf0pmqYUb3F6dBCHGtK5hOM9fTDoZCM/nYxtDiAOKWdJxtxQNXY+u/H4G6GdWGvaD 9Zap4uwFhda0EVKL4QthRcipIWucdYaFRIvi7ZwcUskGpyoFA5JaFxciGKKnGEGq5d JprBxOZBL7enhtdriQv5n1Ay80ZYiPmwmpNUK8IcyjFwxT9hf8wR8QHYWq90+RhEBW op03qWDrCtYNJjTAJJvqiIQ24pXk9db5H/4l+ZwV/eBUe+ju9q6d4Ew6fk17ihdAA/ Ry2gkibrKc9YdhJrSKJZTDqGWdUc7kAjKZ0GDFCJJQyBXQnH8fFlXWZMj7Ez5MVD/H W4O1TW3euUqNg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Ankur Arora , "Paul E . McKenney" , Sebastian Andrzej Siewior , Frederic Weisbecker , Boqun Feng , Sasha Levin , neeraj.upadhyay@kernel.org, joel@joelfernandes.org, josh@joshtriplett.org, urezki@gmail.com, rcu@vger.kernel.org Subject: [PATCH AUTOSEL 6.6 262/294] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Date: Mon, 5 May 2025 18:56:02 -0400 Message-Id: <20250505225634.2688578-262-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505225634.2688578-1-sashal@kernel.org> References: <20250505225634.2688578-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.89 Content-Transfer-Encoding: 8bit From: Ankur Arora [ Upstream commit 83b28cfe796464ebbde1cf7916c126da6d572685 ] With PREEMPT_RCU=n, cond_resched() provides urgently needed quiescent states for read-side critical sections via rcu_all_qs(). One reason why this was needed: lacking preempt-count, the tick handler has no way of knowing whether it is executing in a read-side critical section or not. With (PREEMPT_LAZY=y, PREEMPT_DYNAMIC=n), we get (PREEMPT_COUNT=y, PREEMPT_RCU=n). In this configuration cond_resched() is a stub and does not provide quiescent states via rcu_all_qs(). (PREEMPT_RCU=y provides this information via rcu_read_unlock() and its nesting counter.) So, use the availability of preempt_count() to report quiescent states in rcu_flavor_sched_clock_irq(). Suggested-by: Paul E. McKenney Reviewed-by: Sebastian Andrzej Siewior Signed-off-by: Ankur Arora Reviewed-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng Signed-off-by: Sasha Levin --- kernel/rcu/tree_plugin.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 41021080ad258..dccfc46496393 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -963,13 +963,16 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) */ static void rcu_flavor_sched_clock_irq(int user) { - if (user || rcu_is_cpu_rrupt_from_idle()) { + if (user || rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && + (preempt_count() == HARDIRQ_OFFSET))) { /* * Get here if this CPU took its interrupt from user - * mode or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. + * mode, from the idle loop without this being a nested + * interrupt, or while not holding the task preempt count + * (with PREEMPT_COUNT=y). In this case, the CPU is in a + * quiescent state, so note it. * * No memory barrier is required here because rcu_qs() * references only CPU-local variables that other CPUs -- 2.39.5