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 5816249659; Mon, 14 Oct 2024 14:45:49 +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=1728917149; cv=none; b=aC0zbkP74L3HDRGai+tY/GjvKQhsPE6wy83eDvPcN7sA3w+8LeLcygjZkJ6ivB3TgWBb4lHjWVY+oZgutlFcAzB3TsWp8U3KtcUmNQuskeshSWDbqwdzUQiqEXouosencZXr9AdNO+/PNVH2Em3G3BnXvqRn1jDLjpSzblREsGA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728917149; c=relaxed/simple; bh=kmOmSPRHKlOoK8DY4dPVnJpRSQd+D1KLUXPFupcJBUk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LPTeWAT3QHQ6f0+2DuwE9W/VIF9cLQP91tCwyNqR6832cBeur+3Rr8robx+0CFkRD81y9ibDTsCUtt3MV1wRhYEc8Pn8dvK0D8imUEs4SiMZkRY5RaCk0YEg0SWx1gmWScwXSCrNje43tSWO1ZYwaO0jzu9N61BUdzjKyS7aSUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=rS36l3DJ; 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="rS36l3DJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 718E8C4CEC3; Mon, 14 Oct 2024 14:45:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1728917148; bh=kmOmSPRHKlOoK8DY4dPVnJpRSQd+D1KLUXPFupcJBUk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rS36l3DJzs/al31GsT+fRTF82Qbn0KYTIGVaLaxH0n780X516o8Gd7dLPps9kTD2y RaoqenLoTvPW9w8YQHW2LytgS/7OCo/TI+iQuWCYfXEUHcO17YN9iblQeru7iGHNLp LY7FL2BzJtJ0eV2sPjJm1UKCkIDPbCgypuu0kkfs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, kernel test robot , "Joel Fernandes (Google)" , Frederic Weisbecker , Neeraj Upadhyay , Sasha Levin Subject: [PATCH 6.6 165/213] rcu/nocb: Fix rcuog wake-up from offline softirq Date: Mon, 14 Oct 2024 16:21:11 +0200 Message-ID: <20241014141049.410758881@linuxfoundation.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241014141042.954319779@linuxfoundation.org> References: <20241014141042.954319779@linuxfoundation.org> User-Agent: quilt/0.67 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 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Frederic Weisbecker [ Upstream commit f7345ccc62a4b880cf76458db5f320725f28e400 ] After a CPU has set itself offline and before it eventually calls rcutree_report_cpu_dead(), there are still opportunities for callbacks to be enqueued, for example from a softirq. When that happens on NOCB, the rcuog wake-up is deferred through an IPI to an online CPU in order not to call into the scheduler and risk arming the RT-bandwidth after hrtimers have been migrated out and disabled. But performing a synchronized IPI from a softirq is buggy as reported in the following scenario: WARNING: CPU: 1 PID: 26 at kernel/smp.c:633 smp_call_function_single Modules linked in: rcutorture torture CPU: 1 UID: 0 PID: 26 Comm: migration/1 Not tainted 6.11.0-rc1-00012-g9139f93209d1 #1 Stopper: multi_cpu_stop+0x0/0x320 <- __stop_cpus+0xd0/0x120 RIP: 0010:smp_call_function_single swake_up_one_online __call_rcu_nocb_wake __call_rcu_common ? rcu_torture_one_read call_timer_fn __run_timers run_timer_softirq handle_softirqs irq_exit_rcu ? tick_handle_periodic sysvec_apic_timer_interrupt Fix this with forcing deferred rcuog wake up through the NOCB timer when the CPU is offline. The actual wake up will happen from rcutree_report_cpu_dead(). Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202409231644.4c55582d-lkp@intel.com Fixes: 9139f93209d1 ("rcu/nocb: Fix RT throttling hrtimer armed from offline CPU") Reviewed-by: "Joel Fernandes (Google)" Signed-off-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay Signed-off-by: Sasha Levin --- kernel/rcu/tree_nocb.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 7a0bce3f784df..8993b2322be2b 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -568,13 +568,19 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, rcu_nocb_unlock(rdp); wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY, TPS("WakeLazy")); - } else if (!irqs_disabled_flags(flags)) { + } else if (!irqs_disabled_flags(flags) && cpu_online(rdp->cpu)) { /* ... if queue was empty ... */ rcu_nocb_unlock(rdp); wake_nocb_gp(rdp, false); trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeEmpty")); } else { + /* + * Don't do the wake-up upfront on fragile paths. + * Also offline CPUs can't call swake_up_one_online() from + * (soft-)IRQs. Rely on the final deferred wake-up from + * rcutree_report_cpu_dead() + */ rcu_nocb_unlock(rdp); wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE, TPS("WakeEmptyIsDeferred")); -- 2.43.0