From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx178.postini.com [74.125.245.178]) by kanga.kvack.org (Postfix) with SMTP id 3B41E6B005D for ; Thu, 17 Jan 2013 07:20:07 -0500 (EST) Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 17 Jan 2013 22:15:18 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 56A062CE804A for ; Thu, 17 Jan 2013 23:20:00 +1100 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r0HC8KAL64684056 for ; Thu, 17 Jan 2013 23:08:20 +1100 Received: from d23av03.au.ibm.com (loopback [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r0HCJx9g021378 for ; Thu, 17 Jan 2013 23:19:59 +1100 Message-ID: <50F7EC6B.6030401@linux.vnet.ibm.com> Date: Thu, 17 Jan 2013 20:19:55 +0800 From: Xiao Guangrong MIME-Version: 1.0 Subject: Re: [PATCH] [Patch] mmu_notifier_unregister NULL Pointer deref fix. References: <20130115162956.GH3438@sgi.com> <20130116200018.GA3460@sgi.com> <20130116210124.GB3460@sgi.com> <50F765CC.9040608@linux.vnet.ibm.com> <20130117111213.GM3438@sgi.com> In-Reply-To: <20130117111213.GM3438@sgi.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Robin Holt Cc: Andrea Arcangeli , linux-mm@kvack.org, Wanpeng Li , Avi Kivity , Hugh Dickins , Marcelo Tosatti , Sagi Grimberg , Haggai Eran On 01/17/2013 07:12 PM, Robin Holt wrote: > On Thu, Jan 17, 2013 at 10:45:32AM +0800, Xiao Guangrong wrote: >> On 01/17/2013 05:01 AM, Robin Holt wrote: >>> >>> There is a race condition between mmu_notifier_unregister() and >>> __mmu_notifier_release(). >>> >>> Assume two tasks, one calling mmu_notifier_unregister() as a result >>> of a filp_close() ->flush() callout (task A), and the other calling >>> mmu_notifier_release() from an mmput() (task B). >>> >>> A B >>> t1 srcu_read_lock() >>> t2 if (!hlist_unhashed()) >>> t3 srcu_read_unlock() >>> t4 srcu_read_lock() >>> t5 hlist_del_init_rcu() >>> t6 synchronize_srcu() >>> t7 srcu_read_unlock() >>> t8 hlist_del_rcu() <--- NULL pointer deref. >> >> The detailed code here is: >> hlist_del_rcu(&mn->hlist); >> >> Can mn be NULL? I do not think so since mn is always the embedded struct >> of the caller, it be freed after calling mmu_notifier_unregister. > > If you look at __mmu_notifier_release() it is using hlist_del_init_rcu() > which will set the hlist->pprev to NULL. When hlist_del_rcu() is called, > it attempts to update *hlist->pprev = hlist->next and that is where it > takes the NULL pointer deref. Yes, sorry for my careless. So, That can not be fixed by using hlist_del_init_rcu instead? > >> >>> >>> Tested with this patch applied. My test case which was failing >>> approximately every 300th iteration passed 25,000 tests. >> >> Could you please share your test case? > > I could but it would be very useless. It depends upon having a SGI > UV system with GRUs and and xpmem kernel module loaded. If you would > really like all the bits, I could provide them, but you will not be able > to reproduce the failure. Oh, i see. :) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org