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 9ADEB231A4D; Mon, 2 Jun 2025 14:58:38 +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=1748876318; cv=none; b=phCeijC6UHfjU/KdtD/nmRAWkVtrXoWAyYauLD5lAzyS1jVAifCKHCu8Mk7r3OqqWsKZHkGjhqUXs3fzcIK1D6PTmhRhjWLcN4VlSInMpAqJA1ykXji+ddCcWK9/2UB+Xjq6nWK+uNXaR1PwbLpQzSr9WviCLDWTefAvrtIYIHQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748876318; c=relaxed/simple; bh=4Mh2fBUCEnPhOItJ/EW2D6wNoHEhvChWZlnO2Q71zaQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PiWPVKwdd4CX4yBc12YQowetHksog3Pe0GBg0rfhnu2OdbP//RUDYDcQGJM4+6IydmrijXSfT6aGgTYkfvq5Pg0EcaH3iR58LFK1qDBJpONlrN74uqsKR+oMzTn7OGEdtQu1lnEa0s7VB4tr7R2xZ94LnT7sTv15geqcENPqdMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=WvJWYkV2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="WvJWYkV2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0894FC4CEEB; Mon, 2 Jun 2025 14:58:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748876318; bh=4Mh2fBUCEnPhOItJ/EW2D6wNoHEhvChWZlnO2Q71zaQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WvJWYkV22T7LpUI2KurLlvxbUqBGgjjwWDrWASdCEQqjiMSaWvKvRI4TVqSW3r2uK fQxwupqr/AjmSXz+O2QOOaBdeyZy5mzeyGYeEnhhDEYMBZMDwfB2JOOyoZI59mK0U8 /K+CJu7LJK54wHmC6DbBeJrGBcvaTaCvjxqwSosg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Paul E. McKenney" , Sebastian Andrzej Siewior , Ankur Arora , Frederic Weisbecker , Boqun Feng , Sasha Levin Subject: [PATCH 5.15 139/207] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Date: Mon, 2 Jun 2025 15:48:31 +0200 Message-ID: <20250602134304.169475085@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250602134258.769974467@linuxfoundation.org> References: <20250602134258.769974467@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ 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 b48b42d76474e..9e84d603e882e 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -945,13 +945,16 @@ 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