From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758651Ab1I3OYL (ORCPT ); Fri, 30 Sep 2011 10:24:11 -0400 Received: from rcsinet15.oracle.com ([148.87.113.117]:32922 "EHLO rcsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754624Ab1I3OYJ (ORCPT ); Fri, 30 Sep 2011 10:24:09 -0400 Date: Fri, 30 Sep 2011 10:22:59 -0400 From: Konrad Rzeszutek Wilk To: Jeremy Fitzhardinge , akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Jeremy Fitzhardinge , stable@kernel.org, stefan.bader@canonical.com Subject: Re: Is: [PATCH] x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode. Was: Re: [PATCH] x86/paravirt: Partially revert "remove lazy mode in interrupts" Message-ID: <20110930142259.GA25454@phenom.oracle.com> References: <1317042797-19975-1-git-send-email-konrad.wilk@oracle.com> <4E80A6BD.3070703@goop.org> <20110926193453.GA9717@phenom.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110926193453.GA9717@phenom.oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet22.oracle.com [141.146.126.238] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090204.4E85D0D4.00E6:SCFMA922111,ss=1,re=-4.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > >From 09966678dd645b68a422c9bf0223b13e73387302 Mon Sep 17 00:00:00 2001 > From: Konrad Rzeszutek Wilk > Date: Fri, 23 Sep 2011 17:02:29 -0400 > Subject: [PATCH] x86/paravirt: PTE updates in k(un)map_atomic need to be synchronous, regardless of lazy_mmu mode. > > This patch fixes an outstanding issue that has been reported since 2.6.37. > Under a heavy loaded machine processing "fork()" calls could keepover with: Hm, looks like I forgot to include Andrew on this. Andrew, what is your opinion on this tiny little critical patch? > > BUG: unable to handle kernel paging request at f573fc8c > IP: [] swap_count_continued+0x104/0x180 > *pdpt = 000000002a3b9027 *pde = 0000000001bed067 *pte = 0000000000000000 > Oops: 0000 [#1] SMP > Modules linked in: > Pid: 1638, comm: apache2 Not tainted 3.0.4-linode37 #1 > EIP: 0061:[] EFLAGS: 00210246 CPU: 3 > EIP is at swap_count_continued+0x104/0x180 > .. snip.. > Call Trace: > [] ? __swap_duplicate+0xc2/0x160 > [] ? pte_mfn_to_pfn+0x87/0xe0 > [] ? swap_duplicate+0x14/0x40 > [] ? copy_pte_range+0x45b/0x500 > [] ? copy_page_range+0x195/0x200 > [] ? dup_mmap+0x1c6/0x2c0 > [] ? dup_mm+0xa8/0x130 > [] ? copy_process+0x98a/0xb30 > [] ? do_fork+0x4f/0x280 > [] ? getnstimeofday+0x43/0x100 > [] ? sys_clone+0x30/0x40 > [] ? ptregs_clone+0x15/0x48 > [] ? syscall_call+0x7/0xb > > The problem is that in copy_page_range we turn lazy mode on, and then > in swap_entry_free we call swap_count_continued which ends up in: > > map = kmap_atomic(page, KM_USER0) + offset; > > and then later we touch *map. > > Since we are running in batched mode (lazy) we don't actually set up the > PTE mappings and the kmap_atomic is not done synchronously and ends up > trying to dereference a page that has not been set. > > Looking at kmap_atomic_prot_pfn, it uses 'arch_flush_lazy_mmu_mode' and > doing the same in kmap_atomic_prot and __kunmap_atomic makes the problem > go away. > > Interestingly, git commit b8bcfe997e46150fedcc3f5b26b846400122fdd9 > removed part of this to fix an interrupt issue - but it went to far > and did not consider this scenario. > > CC: Thomas Gleixner > CC: Ingo Molnar > CC: "H. Peter Anvin" > CC: x86@kernel.org > CC: Peter Zijlstra > CC: Jeremy Fitzhardinge > CC: stable@kernel.org > [v1: Redid the commit description per Jeremy's apt suggestion] > Signed-off-by: Konrad Rzeszutek Wilk > --- > arch/x86/mm/highmem_32.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c > index b499626..f4f29b1 100644 > --- a/arch/x86/mm/highmem_32.c > +++ b/arch/x86/mm/highmem_32.c > @@ -45,6 +45,7 @@ void *kmap_atomic_prot(struct page *page, pgprot_t prot) > vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); > BUG_ON(!pte_none(*(kmap_pte-idx))); > set_pte(kmap_pte-idx, mk_pte(page, prot)); > + arch_flush_lazy_mmu_mode(); > > return (void *)vaddr; > } > @@ -88,6 +89,7 @@ void __kunmap_atomic(void *kvaddr) > */ > kpte_clear_flush(kmap_pte-idx, vaddr); > kmap_atomic_idx_pop(); > + arch_flush_lazy_mmu_mode(); > } > #ifdef CONFIG_DEBUG_HIGHMEM > else { > -- > 1.7.4.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/