linux-kernel - Re: [PATCH 4/9] jump label: Fix deadlock b/w jump_label_mutex vs. text

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Date:	Fri, 15 Oct 2010 22:25:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Jason Baron <jbaron@...hat.com>
Subject: Re: [PATCH 4/9] jump label: Fix deadlock b/w jump_label_mutex vs.
 text_mutex

On Fri, 2010-10-15 at 22:55 +0200, Peter Zijlstra wrote:
> On Fri, 2010-10-15 at 16:09 -0400, Steven Rostedt wrote:
> > +void jump_label_lock(void)
> > +{
> > +       mutex_lock(&jump_label_mutex);
> > +}
> > +
> 
> > +++ b/kernel/kprobes.c
> > @@ -1145,13 +1145,16 @@ int __kprobes register_kprobe(struct kprobe *p)
> >                 return ret;
> >  
> >         preempt_disable();
> > +       jump_label_lock();
> 
> How exactly does that work?
> 

This patch should fix it (compiled tested only). If all agree, I'll add
it to the series.

-- Steve

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d45d72e..0dbd328 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1144,17 +1144,13 @@ int __kprobes register_kprobe(struct kprobe *p)
 	if (ret)
 		return ret;
 
-	preempt_disable();
 	jump_label_lock();
+	preempt_disable();
 	if (!kernel_text_address((unsigned long) p->addr) ||
 	    in_kprobes_functions((unsigned long) p->addr) ||
 	    ftrace_text_reserved(p->addr, p->addr) ||
-	    jump_label_text_reserved(p->addr, p->addr)) {
-		preempt_enable();
-		jump_label_unlock();
-		return -EINVAL;
-	}
-	jump_label_unlock();
+	    jump_label_text_reserved(p->addr, p->addr))
+		goto fail_with_jump_label;
 
 	/* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
 	p->flags &= KPROBE_FLAG_DISABLED;
@@ -1168,10 +1164,9 @@ int __kprobes register_kprobe(struct kprobe *p)
 		 * We must hold a refcount of the probed module while updating
 		 * its code to prohibit unexpected unloading.
 		 */
-		if (unlikely(!try_module_get(probed_mod))) {
-			preempt_enable();
-			return -EINVAL;
-		}
+		if (unlikely(!try_module_get(probed_mod)))
+			goto fail_with_jump_label;
+
 		/*
 		 * If the module freed .init.text, we couldn't insert
 		 * kprobes in there.
@@ -1179,11 +1174,11 @@ int __kprobes register_kprobe(struct kprobe *p)
 		if (within_module_init((unsigned long)p->addr, probed_mod) &&
 		    probed_mod->state != MODULE_STATE_COMING) {
 			module_put(probed_mod);
-			preempt_enable();
-			return -EINVAL;
+			goto fail_with_jump_label;
 		}
 	}
 	preempt_enable();
+	jump_label_unlock();
 
 	p->nmissed = 0;
 	INIT_LIST_HEAD(&p->list);
@@ -1225,6 +1220,11 @@ out:
 		module_put(probed_mod);
 
 	return ret;
+
+fail_with_jump_label:
+	preempt_enable();
+	jump_label_unlock();
+	return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(register_kprobe);
 


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