From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (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 A064E4E1C4; Mon, 11 Mar 2024 16:09:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710173352; cv=none; b=ps20j/DN+3yHXdQrh1ZHODSRB5iTampoqm35MF/9VuzF8+KI25SHwospOjjWLh/5Ip2areWSVePKftvBfHkjwVWN5IhcoEQWaFg0/HaUJ85ykpILSUh+E5PgJsXUToQ/HbWvPSbexIkO0scQpzaaDMRjVUw4OP9WXfbVrhfADcQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710173352; c=relaxed/simple; bh=kTp7lbSnNsLXpKG9Si9MQlEjAV3o+Nw/JNd9X+rl1zw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ht2eFDibDDlCwkVuBE9RsjyWh9qZopN7OmRyoipJNmWXn9Ue9Hh5LWVPRZYk1vOBsbX3gbxN44W7Pwas5ZGDDCgaJUTokWu9M77jUtjpuKqezoXzU1bIrxDQlA7xW1nKlNC4SJW9sfZfx570/jfvtG57obVp9YQ+ix5necckEiI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=aH/jcMKr; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="aH/jcMKr" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WxV7yBtzK9mHqXYf7INRFe7VyuknYzJqDnF8rARYuuw=; b=aH/jcMKr2anfzzBa3l1TDS7A17 sb/8qSMaWZSrxaZnGuefRe67F3Nbf1yynHQ7WZRjOmr+WiGYSSIu3CGqVuO/CG5EF4647VGuqhXJr DuOei5PL7SLgcHhTZJcEPKOYx1UE6bESD/4bq2iIMOdpq2TajGQIcHdEKaJCb0Y5IouE1kq5uoFfI dROfwL8BGaAp91Vt9L85/gIUtRDGignUMVkz0pmY5LGiaiLH7IgQQJoH9mGs1R9jMKAzDRUtCIODt 61vc+HIx/q1B9uYBMqJUWhhVLNkvfYHK4SU8/yaKuH83g484P3dfyAQjyYy8lgGciToNJyIxSwoi4 QnkKNCtA==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:60498) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rjiCw-0005QN-0o; Mon, 11 Mar 2024 16:08:58 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rjiCt-0002iw-Ay; Mon, 11 Mar 2024 16:08:55 +0000 Date: Mon, 11 Mar 2024 16:08:55 +0000 From: "Russell King (Oracle)" To: Stefan Wiehler Cc: "Paul E. McKenney" , Joel Fernandes , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm: smp: Avoid false positive CPU hotplug Lockdep-RCU splat Message-ID: References: <20240307160951.3607374-1-stefan.wiehler@nokia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240307160951.3607374-1-stefan.wiehler@nokia.com> Sender: Russell King (Oracle) On Thu, Mar 07, 2024 at 05:09:51PM +0100, Stefan Wiehler wrote: > With CONFIG_PROVE_RCU_LIST=y and by executing > > $ echo 0 > /sys/devices/system/cpu/cpu1/online > > one can trigger the following Lockdep-RCU splat on ARM: > > ============================= > WARNING: suspicious RCU usage > 6.8.0-rc7-00001-g0db1d0ed8958 #10 Not tainted > ----------------------------- > kernel/locking/lockdep.c:3762 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > RCU used illegally from offline CPU! > rcu_scheduler_active = 2, debug_locks = 1 > no locks held by swapper/1/0. > > stack backtrace: > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.8.0-rc7-00001-g0db1d0ed8958 #10 > Hardware name: Allwinner sun8i Family > unwind_backtrace from show_stack+0x10/0x14 > show_stack from dump_stack_lvl+0x60/0x90 > dump_stack_lvl from lockdep_rcu_suspicious+0x150/0x1a0 > lockdep_rcu_suspicious from __lock_acquire+0x11fc/0x29f8 > __lock_acquire from lock_acquire+0x10c/0x348 > lock_acquire from _raw_spin_lock_irqsave+0x50/0x6c > _raw_spin_lock_irqsave from check_and_switch_context+0x7c/0x4a8 > check_and_switch_context from arch_cpu_idle_dead+0x10/0x7c > arch_cpu_idle_dead from do_idle+0xbc/0x138 > do_idle from cpu_startup_entry+0x28/0x2c > cpu_startup_entry from secondary_start_kernel+0x11c/0x124 > secondary_start_kernel from 0x401018a0 > > The CPU is already reported as offline from RCU perspective in > cpuhp_report_idle_dead() before arch_cpu_idle_dead() is invoked. Above > RCU-Lockdep splat is then triggered by check_and_switch_context() acquiring the > ASID spinlock. > > Avoid the false-positive Lockdep-RCU splat by briefly reporting the CPU as > online again while the spinlock is held. > > Signed-off-by: Stefan Wiehler So what do I do about this? I see you submitted this to the patch system on the 8th March, but proposed a different approach on the 9th March. I don't see evidence that Paul is happy with the original approach either and there's no ack/r-b's on anything here. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!