From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756041AbbIBTFP (ORCPT ); Wed, 2 Sep 2015 15:05:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38556 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755419AbbIBTFO (ORCPT ); Wed, 2 Sep 2015 15:05:14 -0400 Date: Wed, 2 Sep 2015 20:05:12 +0100 From: "Richard W.M. Jones" To: Thomas Gleixner Cc: Chuck Ebbert , linux-kernel@vger.kernel.org, x86@kernel.org, Ingo Molnar , "H. Peter Anvin" Subject: Re: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler Message-ID: <20150902190512.GG29283@redhat.com> References: <20150830223757.6e4c5c02@as> <20150901062022.GA19002@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 02, 2015 at 11:11:55AM +0200, Thomas Gleixner wrote: > On Tue, 1 Sep 2015, Richard W.M. Jones wrote: > > On Sun, Aug 30, 2015 at 10:37:57PM -0400, Chuck Ebbert wrote: > > > This is from https://bugzilla.redhat.com/show_bug.cgi?id=1258223 > > > > > > [ 0.036000] BUG: unable to handle kernel paging request at 55501e06 > > [...] > > > [ 0.036000] [] ? add_nops+0x90/0xa0 > > > [ 0.036000] [] apply_alternatives+0x274/0x630 > > > [ 0.036000] [] ? wait_for_xmitr+0xa0/0xa0 > > > [ 0.036000] [] ? sprintf+0x1c/0x20 > > > [ 0.036000] [] ? irq_entries_start+0x698/0x698 > > > [ 0.036000] [] ? memcpy+0xb/0x30 > > > [ 0.036000] [] ? serial8250_set_termios+0x20/0x20 > > [...] > > > Interrupt 0x30 occurred while the alternatives code was replacing the > > > initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the optimized > > > version, 0x8d,0x76,0x00. Only the first byte has been replaced so far, > > > and it makes a mess out of the insn decoding. > > apply_alternatives() has two ways to modify the code: > > 1) text_poke_early() > > 2) optimize_nops() > > The former disables interrupts, the latter not. The patch below should > fix the issue. It has gone through about 1100 iterations so far without hitting the bug. I'll leave it running overnight. Rich. > Thanks, > > tglx > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index c42827eb86cf..6a2f93e029f4 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -257,6 +257,9 @@ void __init arch_init_ideal_nops(void) > /* Use this to add nops to a buffer, then text_poke the whole buffer. */ > static void __init_or_module add_nops(void *insns, unsigned int len) > { > + unsigned long flags; > + > + local_irq_save(flags); > while (len > 0) { > unsigned int noplen = len; > if (noplen > ASM_NOP_MAX) > @@ -265,6 +268,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len) > insns += noplen; > len -= noplen; > } > + local_irq_restore(flags); > } > > extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; > > > -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html