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 E5A08C54E5D for ; Tue, 12 Mar 2024 22:40:09 +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=MXk4ewdRFx0gOxY+EGw4DK29MrqEnKRITOvfEbAcPzo=; b=J2UHVzyTstYAHj 5vK7Z+y/QSZpfY68azLEo2Di6erT/NcktioqYd8lykW/mFZj6cnmHgVFkRCCZxKtc7ELnkLFjIc1l 5nmDZa4mVK/rpIPaY1ZfhOflL+c2ad+g5l3MvRVI4KkAjyrOSsm0FIbrw4eeKz/zqwBjcC5jdX5Aw a5lVxXZw7eaIOAadW9Al/V4KOq3Epe/pZXVZ+/FzktX9NdXiiHYM8XEFr0s4xBeK2KmIx7KCNXjEu WVQaketoB4FYqx7OIZnMrFwNUTTmtd/pgEHWjdjXdmTJcHA9n2eXQtNFwAfizdsSHrBUcrEUyHlQx HmzNxnvsIFsC6nyuoq2w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rkAmp-00000007sNs-1aNR; Tue, 12 Mar 2024 22:39:55 +0000 Received: from pandora.armlinux.org.uk ([2001:4d48:ad52:32c8:5054:ff:fe00:142]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1rkAml-00000007sM6-3Vee for linux-arm-kernel@lists.infradead.org; Tue, 12 Mar 2024 22:39:53 +0000 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=IW00bxPf22nPInwkJFq4lSI3c2JyJKalEpfx3FB1zio=; b=c2HsHfC6XSjDkTcQwXA2jzOKXe LzloQp8SVaLEZtyEuGkEJapALmFdG04UCmtczVakGuFATt2K1heprGge0+y2Z+kBJMgmc8EgeEKp2 M4WKy/XAXnXwnibshvD+64inMS/ccfRe1uZ4gpIf543TGcFObvQY7BIFFyGXNqX2No0jk7eY1uqNM y/zTSzWKlE6BONMolApzpEtxgoc6oLbC+nkWL1gmFHy6mEa6CmJSVsKhNpP0H1ZN6V678KOHA2Je7 /6FtbSlP5M8L2IbJq0rNP0GjkVfvneoxMOo6O3sRB+rxDidLXT/FpadKFLtj9tmHW4iNSoYh2E9bL OqAOpAoA==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:45008) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rkAmV-00072y-1h; Tue, 12 Mar 2024 22:39:35 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rkAmQ-0003uo-NL; Tue, 12 Mar 2024 22:39:30 +0000 Date: Tue, 12 Mar 2024 22:39:30 +0000 From: "Russell King (Oracle)" To: Will Deacon 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: References: <20240307160951.3607374-1-stefan.wiehler@nokia.com> <66fdce3a-c7f6-4ef4-ab56-7c9ece0b00e2@nokia.com> <20240312221440.GA29419@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20240312221440.GA29419@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240312_153951_947202_8C9B6CB0 X-CRM114-Status: GOOD ( 24.55 ) 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 On Tue, Mar 12, 2024 at 10:14:40PM +0000, Will Deacon wrote: > 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... As the init_mm shouldn't have any userspace mappings, isn't the ASID entirely redundant? Couldn't check_and_switch_context() just simply do the vmalloc seq check, set the reserved ASID, and then head to switch_mm_fastpath to call the mm switch code? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel