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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 73A52C25B08 for ; Wed, 17 Aug 2022 05:49:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234019AbiHQFtq (ORCPT ); Wed, 17 Aug 2022 01:49:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230085AbiHQFto (ORCPT ); Wed, 17 Aug 2022 01:49:44 -0400 Received: from mail.wantstofly.org (hmm.wantstofly.org [213.239.204.108]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 145077C51D for ; Tue, 16 Aug 2022 22:49:43 -0700 (PDT) Received: by mail.wantstofly.org (Postfix, from userid 1000) id 3A1E97F54A; Wed, 17 Aug 2022 08:49:40 +0300 (EEST) Date: Wed, 17 Aug 2022 08:49:40 +0300 From: Lennert Buytenhek To: Baolu Lu Cc: Bart Van Assche , Sasha Levin , David Woodhouse , Joerg Roedel , iommu@lists.linux.dev, Will Deacon , Robin Murphy , Kevin Tian , Ashok Raj , Christoph Hellwig , Jason Gunthorpe , Liu Yi L , Jacob jun Pan , linux-kernel@vger.kernel.org, Scarlett Gourley , James Sewart , Jack O'Sullivan Subject: Re: lockdep splat due to klist iteration from atomic context in Intel IOMMU driver Message-ID: References: <5f734387-9757-0670-3eef-b565116af541@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5f734387-9757-0670-3eef-b565116af541@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 17, 2022 at 12:45:26PM +0800, Baolu Lu wrote: > > > On a build of 7ebfc85e2cd7 ("Merge tag 'net-6.0-rc1' of > > > git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net"), with > > > CONFIG_INTEL_IOMMU_DEBUGFS enabled, I am seeing the lockdep splat > > > below when an I/O page fault occurs on a machine with an Intel > > > IOMMU in it. > > > > > > The issue seems to be the klist iterator functions using > > > spin_*lock_irq*() but the klist insertion functions using > > > spin_*lock(), combined with the Intel DMAR IOMMU driver iterating > > > over klists from atomic (hardirq) context as of commit 8ac0b64b9735 > > > ("iommu/vt-d: Use pci_get_domain_bus_and_slot() in pgtable_walk()") > > > when CONFIG_INTEL_IOMMU_DEBUGFS is enabled, where > > > pci_get_domain_bus_and_slot() calls into bus_find_device() which > > > iterates over klists. > > > > > > I found this commit from 2018: > > > > > >     commit 624fa7790f80575a4ec28fbdb2034097dc18d051 > > >     Author: Bart Van Assche > > >     Date:   Fri Jun 22 14:54:49 2018 -0700 > > > > > >         scsi: klist: Make it safe to use klists in atomic context > > > > > > This commit switched lib/klist.c:klist_{prev,next} from > > > spin_{,un}lock() to spin_{lock_irqsave,unlock_irqrestore}(), but left > > > the spin_{,un}lock() calls in add_{head,tail}() untouched. > > > > > > The simplest fix for this would be to switch > > > lib/klist.c:add_{head,tail}() > > > over to use the IRQ-safe spinlock variants as well? > > > > Another possibility would be to evaluate whether it is safe to revert > > commit 624fa7790f80 ("scsi: klist: Make it safe to use klists in atomic > > context"). That commit is no longer needed by the SRP transport driver > > since the legacy block layer has been removed from the kernel. > > If so, pci_get_domain_bus_and_slot() can not be used in this interrupt > context, right? The 624fa7790f80 commit from 2018 tried to make klist use safe from atomic context, but since it missed a few of the klist accessors, it didn't actually manage to make it safe, so it's already not safe to use pci_get_domain_bus_and_slot() from interrupt context right now, even without reverting this commit. Reverting the commit would just be a declaration that klist use from atomic context isn't safe and never was. A quick check doesn't turn up any other cases where people have run into this issue with code in mainline, so it would seem that the newly-added use of pci_get_domain_bus_and_slot() to the iommu/vt-d fault reporting interrupt handler is one of very few (if not only) cases of mainline code wanting to access klists from atomic context. Kind regards, Lennert