Messages in this thread | | | Date | Tue, 3 Mar 2009 15:53:12 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Text Edit Lock - kprobes architecture independent support (v2) |
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* Ananth N Mavinakayanahalli <ananth@in.ibm.com> wrote:
> On Tue, Mar 03, 2009 at 10:27:50AM +0100, Ingo Molnar wrote: > > > > * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> 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
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