From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: vunmap() on large regions may trigger soft lockup warnings Date: Mon, 16 Dec 2013 12:56:13 +0000 Message-ID: <52AEF86D.808@citrix.com> References: <52A899AB.3010506@citrix.com> <20131211133917.dd10cb2c4360dba65d8e6ce2@linux-foundation.org> <52A9B127.9010501@citrix.com> <20131214003208.f99bc37c.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20131214003208.f99bc37c.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org To: Andrew Morton Cc: "linux-kernel@vger.kernel.org" , Len Brown , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, xen-devel , Dietmar Hahn List-Id: linux-acpi@vger.kernel.org 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? David