From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756284AbZCCMHN (ORCPT ); Tue, 3 Mar 2009 07:07:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751139AbZCCMG7 (ORCPT ); Tue, 3 Mar 2009 07:06:59 -0500 Received: from e3.ny.us.ibm.com ([32.97.182.143]:52858 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751077AbZCCMG6 (ORCPT ); Tue, 3 Mar 2009 07:06:58 -0500 Date: Tue, 3 Mar 2009 17:36:59 +0530 From: Ananth N Mavinakayanahalli To: Ingo Molnar Cc: Mathieu Desnoyers , Peter Zijlstra , Masami Hiramatsu , Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" , Steven Rostedt Subject: Re: [PATCH] Text Edit Lock - kprobes architecture independent support (v2) Message-ID: <20090303120659.GA3480@in.ibm.com> Reply-To: ananth@in.ibm.com References: <49AC5A87.7000604@redhat.com> <20090302222254.GA31962@elte.hu> <49AC63FA.70801@redhat.com> <20090302230915.GA11626@elte.hu> <49AC6DEA.2050304@redhat.com> <20090302234910.GA17956@elte.hu> <20090303000054.GC3906@Krystal> <20090303003237.GA30221@elte.hu> <20090303013124.GB7783@Krystal> <20090303092750.GG11484@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090303092750.GG11484@elte.hu> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 03, 2009 at 10:27:50AM +0100, Ingo Molnar wrote: > > * Mathieu Desnoyers wrote: > > > @@ -709,7 +711,8 @@ int __kprobes register_kprobe(struct kpr Hi Ingo, > > if (kprobe_enabled) > > arch_arm_kprobe(p); > > hm, it's cleaner now, but there's serious locking dependency > problems visible in the patch: > > > - > > +out_unlock_text: > > + mutex_unlock(&text_mutex); > > out: > > mutex_unlock(&kprobe_mutex); > > this one creates a (text_mutex -> kprobe_mutex) dependency. > (also you removed a newline spuriously - dont do that) That is a mutex_unlock :-) ... > > @@ -746,8 +749,11 @@ valid_p: > > * enabled and not gone - otherwise, the breakpoint would > > * already have been removed. We save on flushing icache. > > */ > > - if (kprobe_enabled && !kprobe_gone(old_p)) > > + if (kprobe_enabled && !kprobe_gone(old_p)) { > > + mutex_lock(&text_mutex); > > arch_disarm_kprobe(p); > > + mutex_unlock(&text_mutex); > > + } > > hlist_del_rcu(&old_p->hlist); > > (kprobe_mutex -> text_mutex) dependency. AB-BA deadlock. At this time the kprobe_mutex is already held. ... > > @@ -1280,12 +1285,14 @@ static void __kprobes enable_all_kprobes > > if (kprobe_enabled) > > goto already_enabled; > > > > + mutex_lock(&text_mutex); > > for (i = 0; i < KPROBE_TABLE_SIZE; i++) { > > head = &kprobe_table[i]; > > hlist_for_each_entry_rcu(p, node, head, hlist) > > if (!kprobe_gone(p)) > > arch_arm_kprobe(p); > > } > > + mutex_unlock(&text_mutex); > > this one creates a (kprobe_mutex -> text_mutex) dependency > again. kprobe_mutex his held here too... > > @@ -1310,6 +1317,7 @@ static void __kprobes disable_all_kprobe > > > > kprobe_enabled = false; > > printk(KERN_INFO "Kprobes globally disabled\n"); > > + mutex_lock(&text_mutex); > > for (i = 0; i < KPROBE_TABLE_SIZE; i++) { > > head = &kprobe_table[i]; > > hlist_for_each_entry_rcu(p, node, head, hlist) { > > @@ -1317,7 +1325,7 @@ static void __kprobes disable_all_kprobe > > arch_disarm_kprobe(p); > > } > > } > > - > > + mutex_unlock(&text_mutex); > > mutex_unlock(&kprobe_mutex); > > And this one in the reverse direction again. Unlock again :-) > The dependencies are totally wrong. The text lock (a low level > lock) should nest inside the kprobes mutex (which is the higher > level lock). >>From what I see, Mathieu has done just that and has gotten the order right in all cases. Or maybe I am missing something? (I recall having tested this patch with LOCKDEP turned on and it din't throw any errors). Ananth