Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756119AbZCCOy1 (ORCPT ); Tue, 3 Mar 2009 09:54:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755438AbZCCOyR (ORCPT ); Tue, 3 Mar 2009 09:54:17 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:47365 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751897AbZCCOyQ (ORCPT ); Tue, 3 Mar 2009 09:54:16 -0500 Date: Tue, 3 Mar 2009 15:53:12 +0100 From: Ingo Molnar To: Ananth N Mavinakayanahalli 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: <20090303145312.GA19483@elte.hu> References: <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> <20090303120659.GA3480@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090303120659.GA3480@in.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3075 Lines: 100 * Ananth N Mavinakayanahalli wrote: > 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? No, it's fine indeed, i got the locking order messed up ... twice :-) Ingo -- 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/