From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 12701559CAB for ; Wed, 9 Sep 2026 12:37:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788957423; cv=none; b=dMubTZS+fgsiEtTm35frELeIa7MgwHxLms0J3Cw2xB/chOfaPWP75sL1kr7X8ww0XWWB+5Z5rTHeqIFeWUQ5wZO+i9JQONuipScLrbN61GU22d1SZKDrVmdUAjoLpdGMBRiV1sCTT9aTHITYkp2pqgsPAAtGXxuUEYVltZxF7hs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788957423; c=relaxed/simple; bh=hzkyidTZn0frPGQyURwsWDb22YJiSdj3NnXQtBPy6gw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GvCKfNs6XzctTwRM3lQ3DsgoFBxvf1w23eD937QS0+70o9zEdoBO9JCszfJ3ishJ99B3+LddwwWXTTY+HDgcfrXLTc2jfTYH0dJYkmCkJI5nqySSWmOjXIOAvmJLEhol+/N2hQ7vXEtU+1TG9+N3AwvyDsOqEwC2sO1b4Iu43Qk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S4/1pmTA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="S4/1pmTA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90F2F1F00A3A; Wed, 9 Sep 2026 12:36:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788957421; bh=KbGwZADL5Y87oVCXzEkLYxGUDy1vvUC8dlGfMGpBVDI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=S4/1pmTA5TeeJmbyHhM3d6gQdjVAJmfXI+A6HeJrf+afK7asfVmvlItVWZEFGDBQg 71eUFp6E0mq0/e1RMn2MgswsOK5xn0rrxmzaSRZasThhE2d6/hK8gdHc4/mqo4jwjY 5Gtw0m/xY9mu5COxp4wtvTKdk6Q6OCz9RSNjzmyMoj2uxIJ+n0g3rDkykvUI7YbpIA IbPfM5rQghACN+rECUcOzXzw2jwAjOBp3xlRGkUGu1o0x6E07SFnKuoctsGqtIEsel oPbtusK8tUXl6ORQd9Bj/1jze3/5eigC6uGb3nz9w6iLm/En1mhwJEZF4kagb+YDof 5tjONB8OAYbjA== Date: Wed, 9 Sep 2026 13:36:55 +0100 From: Will Deacon To: Jinjie Ruan Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Catalin Marinas , Borislav Petkov , Lorenzo Pieralisi , Mark Rutland , David Woodhouse , Peter Zijlstra , Marc Zyngier Subject: Re: [PATCH 09/19] arm64: smp: Defer RCU registration during secondary CPU bringup Message-ID: References: <20260907164024.17164-1-will@kernel.org> <20260907164024.17164-10-will@kernel.org> <45c37592-f05d-4b1c-812b-0cb38d1c3e24@huawei.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Sep 08, 2026 at 07:25:54PM +0800, Jinjie Ruan wrote: > 在 2026/9/8 18:19, Will Deacon 写道: > > On Tue, Sep 08, 2026 at 04:55:36PM +0800, Jinjie Ruan wrote: > >> I think we need to handle the printk problem before this patch as we > >> discussed earlier. > >> > >> Otherwise defer the rcutree_report_cpu_starting() will trigger a > >> false-positive lockdep"suspicious RCU usage" splat during early lock > >> acquisitions as commit ce3d31ad3cac ("arm64/smp: Move > >> rcu_cpu_starting() earlier") pointed out. > > > > Sorry, I meant to mention this in the cover letter but forgot about it. > > I'm not sure that ce3d31ad3cac ("arm64/smp: Move rcu_cpu_starting() > > earlier") is still relevant with the latest printk/console/lockdep code. > > I tried quite hard to trigger lockdep splats manually, but the only way > > I could do it was by using the "%pS" specifier to print the name of a > > symbol in a module, which would cause an RCU walk of the module symbols > > in the kallsyms code! Manually calling WARN() or even rcu_read_lock() / > > spin_lock() did _not_ trigger a splat. > > Add "dyndbg="+p"" in cmdline, CONFIG_DEBUG_LOCK_ALLOC=y, > CONFIG_PROVE_RCU_LIST=y, we can reproduce the warning as below: > > I believe there is also a problem in the RISC-V code itself here as > store_cpu_topology() is common for RISC-V. > > [ 0.335162] smp: Bringing up secondary CPUs ... > [ 0.345495] > [ 0.345513] ============================= > [ 0.345523] WARNING: suspicious RCU usage > [ 0.345621] 7.3.0-rc2-00010-g2311ba2cd56f #500 Tainted: G W > [ 0.345637] ----------------------------- > [ 0.345646] kernel/locking/lockdep.c:3845 RCU-list traversed in > non-reader section!! > [ 0.345659] > [ 0.345659] other info that might help us debug this: > [ 0.345659] > [ 0.345680] > [ 0.345680] RCU used illegally from offline CPU! > [ 0.345680] rcu_scheduler_active = 1, debug_locks = 1 > [ 0.345725] locks held by swapper/1/0: 0, last CPU#1 > [ 0.345743] > [ 0.345743] stack backtrace: > [ 0.345834] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G W > 7.3.0-rc2-00010-g2311ba2cd56f #500 PREEMPT(full) > [ 0.345885] Tainted: [W]=WARN > [ 0.346077] Call trace: > [ 0.346102] show_stack+0x20/0x38 (C) > [ 0.346153] dump_stack_lvl+0xc4/0x150 > [ 0.346176] dump_stack+0x18/0x28 > [ 0.346194] lockdep_rcu_suspicious+0x170/0x238 > [ 0.346217] __lock_acquire+0xf08/0x1818 > [ 0.346237] lock_acquire+0x1e0/0x450 > [ 0.346256] _raw_spin_lock_irqsave+0x70/0xc0 > [ 0.346277] down_trylock+0x20/0x60 > [ 0.346293] __down_trylock_console_sem+0x4c/0x118 > [ 0.346316] vprintk_emit+0x2d8/0x3f8 > [ 0.346333] vprintk_default+0x40/0x58 > [ 0.346350] vprintk+0x3c/0x80 > [ 0.346366] _printk+0x64/0x98 > [ 0.346386] __dynamic_pr_debug+0x90/0xd8 > [ 0.346406] acpi_get_cache_info+0x140/0x1a0 > [ 0.346430] init_cache_level+0xec/0x110 > [ 0.346450] detect_cache_attributes+0x74/0x7c0 > [ 0.346473] update_siblings_masks+0x30/0x300 > [ 0.346495] store_cpu_topology+0x70/0xf0 > [ 0.346515] secondary_start_kernel+0xe0/0x178 > [ 0.346535] __secondary_switched+0xc0/0xc8 I was about to say "don't do this" but then I realised two things: 1. update_siblings_masks() can trigger lockdep splats outside of pr_debug() if RCU isn't up and running, e.g.: [ 0.524042] show_stack+0x18/0x24 (C) [ 0.524519] __dump_stack+0x28/0x38 [ 0.524546] dump_stack_lvl+0x64/0x84 [ 0.524562] dump_stack+0x18/0x24 [ 0.524576] lockdep_rcu_suspicious+0x134/0x1cc [ 0.524591] __lock_acquire+0xee8/0x2cb0 [ 0.524606] lock_acquire+0x11c/0x2fc [ 0.524621] _raw_spin_lock_irqsave+0x64/0x84 [ 0.524641] of_find_property+0x2c/0x8c [ 0.524659] detect_cache_attributes+0x1c0/0x6d0 [ 0.524676] update_siblings_masks+0x38/0x288 [ 0.524692] store_cpu_topology+0x4c/0x58 [ 0.524706] secondary_start_kernel+0xdc/0x1c8 [ 0.524722] __secondary_switched+0x120/0x124 2. This code is running _after_ cpuhp_ap_sync_alive(). So for the next version, I'll reintroduce the call to rcutree_report_cpu_starting(), but move it immediately after the call to cpuhp_ap_sync_alive(). I think that will solve these issues, without causing issues with the concurrent part of early boot and also without reintroducing the early call to rcutree_report_cpu_dead(). Cheers, Will