From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: vunmap() on large regions may trigger soft lockup warnings Date: Mon, 16 Dec 2013 14:57:17 -0800 Message-ID: <20131216145717.f6e2bca5adc8730fad523fb2@linux-foundation.org> References: <52A899AB.3010506@citrix.com> <20131211133917.dd10cb2c4360dba65d8e6ce2@linux-foundation.org> <52A9B127.9010501@citrix.com> <20131214003208.f99bc37c.akpm@linux-foundation.org> <52AEF86D.808@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:46474 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750935Ab3LPW5T (ORCPT ); Mon, 16 Dec 2013 17:57:19 -0500 In-Reply-To: <52AEF86D.808@citrix.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: David Vrabel Cc: "linux-kernel@vger.kernel.org" , Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, xen-devel , Dietmar Hahn , Huang Ying , Mauro Carvalho Chehab On Mon, 16 Dec 2013 12:56:13 +0000 David Vrabel wrote: > On 14/12/13 08:32, Andrew Morton wrote: > > On Thu, 12 Dec 2013 12:50:47 +0000 David Vrabel wrote: > > > >>> each time. But that would require difficult tuning of N. > >>> > >>> I suppose we could just do > >>> > >>> if (!in_interrupt()) > >>> cond_resched(); > >>> > >>> in vunmap_pmd_range(), but that's pretty specific to ghes.c and doesn't > >>> permit unmap-inside-spinlock. > >>> > >>> So I can't immediately think of a suitable fix apart from adding a new > >>> unmap_kernel_range_atomic(). Then add a `bool atomic' arg to > >>> vunmap_page_range() and pass that all the way down. > >> > >> That would work for the unmap, but looking at the GHES driver some more > >> and it looks like it's call to ioremap_page_range() is already unsafe -- > >> it may need to allocate a new PTE page with a non-atomic alloc in > >> pte_alloc_one_kernel(). > >> > >> Perhaps what's needed here is a pair of ioremap_page_atomic() and > >> iounmap_page_atomic() calls? With some prep function to sure the PTE > >> pages (etc.) are preallocated. > > > > Is ghes.c the only problem source here? If so then a suitable solution > > would be to declare that driver hopelessly busted and proceed as if it > > didn't exist :( > > All the other callers do so from non-atomic context. ghes.c is the only > broken caller. > > Shall I resend or are you happy to take the patch off the first email in > this thread? Well first we should attempt to wake up the ghes maintainers and tell them we're about to break their stuff. (Which I believe is already broken). The fix won't be easy - presumably ghes will need to punt all its IRQ- and NMI_context operations up into kernel thread context.