From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A1C54C54E58 for ; Tue, 12 Mar 2024 22:15:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=8wg6QU9Y1VJRmvqhsNGF5kdb/bfnRzuT8qbBY2mpZfg=; b=wEm3ezhujydMnF n9odtONfMpkDmbZ6yNommjY9AMdwUgQiZykRZQd33diX2reGA681y+qKm5w/5doNlBeJ7A9gEptkr PW0DIqGlu39kBosKawR3Qc7yz342Yz3nVOfM9DKZzttOPPJXIsa1aM+NMo9hEa+7m+l2GAEZyu0iq WZCRtGDVpO26zfolJ+nApamI0eFeSd1/rWK00YclMCLbiyBOJ4MqP9AMellMsM9XICF/KY014f6Tb Z885HhXjlgFZdJrL8g2hO5NHWQqLBnIn/RHcZxo3A49gfxZHtPeSXlKZbbzLciosdKxbvLU5l18/c qtcAXJoSdVT+d1o5DlUQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rkAOb-00000007lQM-1Z3w; Tue, 12 Mar 2024 22:14:53 +0000 Received: from sin.source.kernel.org ([2604:1380:40e1:4800::1]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1rkAOY-00000007lOj-11Ir for linux-arm-kernel@lists.infradead.org; Tue, 12 Mar 2024 22:14:51 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id 01AB1CE0189; Tue, 12 Mar 2024 22:14:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C3C44C433F1; Tue, 12 Mar 2024 22:14:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1710281687; bh=4aUjgMILvjcV11Jnjg3n3Tf0x1z42XftzUW2VxACbeI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Y11sc2Qxg4CC2tN7G5D3/b0N7NwRD+M/+MxAgC6/Ksh0pen1bLwvSBO4m+hLBh4sX ma8dAOg/x8ZdmaMPxmb+a2b9Naxgm8vjIOIsfPZyg4PjRZHcw5GP62WnTksV+Q3IBQ /WEQxfktpaDsy6fZ6uhc9KS+dyOVkoENt5w/sayVRbxdzu1nuzXC5V0k6aguddmi8A SUAo81OefwyMb/S8T9FokV9DioatMsgFl3AH2WmpAoEvU7VNRSQX4I1hGHw+4PLncJ o1PTrxU4uQKIpStN219soS6oeHusBmWMsuCc3gEPPb8LptMitjNGhY5K1be8SXsvED 7m/Oziz1P5ZgQ== Date: Tue, 12 Mar 2024 22:14:40 +0000 From: Will Deacon To: "Russell King (Oracle)" Cc: Stefan Wiehler , Joel Fernandes , "Paul E. McKenney" , 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: <20240312221440.GA29419@willie-the-truck> References: <20240307160951.3607374-1-stefan.wiehler@nokia.com> <66fdce3a-c7f6-4ef4-ab56-7c9ece0b00e2@nokia.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240312_151450_659007_7C64BDB0 X-CRM114-Status: GOOD ( 18.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Russell, On Sat, Mar 09, 2024 at 09:57:04AM +0000, Russell King (Oracle) wrote: > On Sat, Mar 09, 2024 at 08:45:35AM +0100, Stefan Wiehler wrote: > > diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c > > index 4204ffa2d104..4fc2c559f1b6 100644 > > --- a/arch/arm/mm/context.c > > +++ b/arch/arm/mm/context.c > > @@ -254,7 +254,8 @@ void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk) > > && atomic64_xchg(&per_cpu(active_asids, cpu), asid)) > > goto switch_mm_fastpath; > > > > - raw_spin_lock_irqsave(&cpu_asid_lock, flags); > > + local_irq_save(flags); > > + arch_spin_lock(&cpu_asid_lock.raw_lock); > > /* Check that our ASID belongs to the current generation. */ > > asid = atomic64_read(&mm->context.id); > > if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) { > > @@ -269,7 +270,8 @@ void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk) > > > > atomic64_set(&per_cpu(active_asids, cpu), asid); > > cpumask_set_cpu(cpu, mm_cpumask(mm)); > > - raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); > > + arch_spin_unlock(&cpu_asid_lock.raw_lock); > > + local_irq_restore(flags); > > > > switch_mm_fastpath: > > cpu_switch_mm(mm->pgd, mm); > > > > @Russell, what do you think? > > I think this is Will Deacon's code, so we ought to hear from Will... Thanks for adding me in. Using arch_spin_lock() really feels like a bodge to me. This code isn't run only on the hot-unplug path, but rather this is part of switch_mm() and we really should be able to have lockdep work properly there for the usual case. Now, do we actually need to worry about the ASID when switching to the init_mm? I'd have thought that would be confined to global (kernel) mappings, so I wonder whether we could avoid this slow path code altogether like we do on arm64 in __switch_mm(). But I must confess that I don't recall the details of the pre-LPAE MMU configuration... Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel