Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754673Ab2E3Nu3 (ORCPT ); Wed, 30 May 2012 09:50:29 -0400 Received: from [192.48.179.30] ([192.48.179.30]:38899 "EHLO relay.sgi.com" rhost-flags-FAIL-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1754500Ab2E3Nu2 (ORCPT ); Wed, 30 May 2012 09:50:28 -0400 Date: Wed, 30 May 2012 08:46:03 -0500 From: Dimitri Sivanich To: Thomas Gleixner Cc: Suresh Siddha , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Yinghai Lu , Naga Chumbalkar , Jacob Pan , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, gregkh@suse.de, stable@vger.kernel.org Subject: Re: [PATCH] x86: check for valid irq_cfg pointer in smp_irq_move_cleanup_interrupt Message-ID: <20120530134603.GA32097@sgi.com> References: <20120523181636.GA2032@sgi.com> <20120523190414.GA5263@sgi.com> <1337801086.1997.197.camel@sbsiddha-desk.sc.intel.com> <20120523200226.GA6936@sgi.com> <1337816970.1997.207.camel@sbsiddha-desk.sc.intel.com> <20120524143711.GA24711@sgi.com> <1337883560.7938.9.camel@sbsiddha-desk.sc.intel.com> <1337991809.7938.36.camel@sbsiddha-desk.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3033 Lines: 79 On Sat, May 26, 2012 at 12:18:21PM +0200, Thomas Gleixner wrote: > On Fri, 25 May 2012, Suresh Siddha wrote: > > On Thu, 2012-05-24 at 21:16 +0200, Thomas Gleixner wrote: > > There are other (not-so common) irq desc references, like in the > > show_interrupts() (cat /proc/interrupts path) etc, that does things like > > this in the process context: > > > > desc = irq_to_desc(i); > > if (!desc) > > return 0; > > > > raw_spin_lock_irqsave(&desc->lock, flags); > > > > May be we should introduce something like > > get_irq_desc_locked()/put_irq_desc_locked() that can safely access the > > irq desc with pre-emption/irq's disabled and lock it etc. And the > > synchronize_sched() will enable the destroy_irq()/free_desc() to free it > > safely etc. > > I want to avoid that and instead use proper refcounting. The reason is > that we want to move the irq descriptor when the affinity changes > nodes, and for that we need refcounting anyway. > While this proposal sounds good, in the meantime would there be any harm in putting the NULL cfg check into smp_irq_move_cleanup_interrupt()? It's a minimal change, and eliminates the panics that I've encountered thus far. Reposting the patch. A NULL pointer dereference can occur in smp_irq_move_cleanup_interrupt() if we haven't yet setup the irq_cfg pointer in the irq_desc.irq_data.chip_data. In create_irq_nr() there is a window where we have set vector_irq in __assign_irq_vector(), but not yet called irq_set_chip_data() to set the irq_cfg pointer. Should an IRQ_MOVE_CLEANUP_VECTOR hit the cpu in question during this time, smp_irq_move_cleanup_interrupt() will attempt to process the aforementioned irq, but panic when accessing irq_cfg. There is also a window in destroy_irq() where we've cleared the irq_cfg pointer in free_irq_cfg(), but have not yet called irq_free_desc(). Note that we have cleared vector_irq in __clear_irq_vector() prior to free_irq_cfg(), but smp_irq_move_cleanup_interrupt() might've already referenced the irq_desc. Only continue processing the irq if irq_cfg is non-NULL. Signed-off-by: Dimitri Sivanich --- arch/x86/kernel/apic/io_apic.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) Index: linux/arch/x86/kernel/apic/io_apic.c =================================================================== --- linux.orig/arch/x86/kernel/apic/io_apic.c +++ linux/arch/x86/kernel/apic/io_apic.c @@ -2478,9 +2478,12 @@ asmlinkage void smp_irq_move_cleanup_int if (!desc) continue; - cfg = irq_cfg(irq); raw_spin_lock(&desc->lock); + cfg = irq_cfg(irq); + if (!cfg) + goto unlock; + /* * Check if the irq migration is in progress. If so, we * haven't received the cleanup request yet for this irq. -- 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/