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 A800E2F6B29; Mon, 5 May 2025 23:17:53 +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=1746487074; cv=none; b=YCZi+3FAjY16s8hW42BnQ6B4+0xtVs0k3G8nswda4QJwpi0okwj54n2O4aourPYy7dJ79S9Jb5pnAq7gdt+EGGr5orIztP8oTXQKbmgihU0Hzk+R9en3Mj3ctaciR2hnaqUqJa2BGMUzocUh4ocopMvZ+sL/4mJhPVsv/sfVT/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746487074; c=relaxed/simple; bh=xSLLz/4eix5InbKfFV8XKKJhByYuDsQyk3B6wkXDwHY=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=oyCicqZr2H+IOUc3IdsNH53iIOWma5EuzqHFBEg0cBRCTNz7+Kq2IhtQ2bdYFvcof/Q+t1qVxTE1x0hx7shxW8AfepJWEXnbIHaEVXbLSaL1M+IQxD3ZtlGwvql8QKBVKbtWTsqLISYUnx+2gynonGlTBStvBPwcK+cZrsDiXeQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=irXGZByO; 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="irXGZByO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C03B6C4CEED; Mon, 5 May 2025 23:17:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746487073; bh=xSLLz/4eix5InbKfFV8XKKJhByYuDsQyk3B6wkXDwHY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=irXGZByOeE0NR8B690YMlm6nRyb8bYnDF1GqztQnfVSNyAM822lYSHCS+PS/wKqni UeGifxkE8wko8hKU9w9WjcaUomfO7HOdRnKEkoyERnr0E+epToTdYYos76rqC6lpZy BOYEHy2BbNd8jckcz7EkflQ8YNEz9nbA6EzZibEbDhZtqlew5yL/EaBRh0+kFLXvoD 4vBISjRYicvM1Gorh3fsqR7nLocL69BRlfj5IWWwfNeDTfAkqdSzAT4zKXGEs6Yfbf wRpvGXoWswecIuGSLg9De/h6pPdkOR8TO2JqbO+CXm+/4MUoW91f4gIEuo+JQDjbgU U6grwGpxRbXYA== 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 5.15 139/153] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Date: Mon, 5 May 2025 19:13:06 -0400 Message-Id: <20250505231320.2695319-139-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250505231320.2695319-1-sashal@kernel.org> References: <20250505231320.2695319-1-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 5.15.181 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 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