linux-kernel - Re: [RFC][PATCH] tracing/module: Move tracepoint out of module.h

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Date:	Thu, 29 Mar 2012 06:22:44 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [RFC][PATCH] tracing/module: Move tracepoint out of module.h

Le mercredi 01 février 2012 à 17:18 +1030, Rusty Russell a écrit :

>  
> +void __module_get(struct module *module)
> +{
> +	if (module) {
> +		preempt_disable();
> +		__this_cpu_inc(module->refptr->incs);
> +		trace_module_get(module, _RET_IP_);
> +		preempt_enable();
> +	}
> +}
> +EXPORT_SYMBOL(__module_get);
> +

Hi Rusty

I am wondering why preempt_disable()/preempt_enable() is needed in this
code.

this_cpu_inc(module->refptr->incs) is preempt safe...



diff --git a/kernel/module.c b/kernel/module.c
index 78ac6ec..7dc88b3 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -907,10 +907,8 @@ static struct module_attribute modinfo_refcnt =
 void __module_get(struct module *module)
 {
 	if (module) {
-		preempt_disable();
-		__this_cpu_inc(module->refptr->incs);
+		this_cpu_inc(module->refptr->incs);
 		trace_module_get(module, _RET_IP_);
-		preempt_enable();
 	}
 }
 EXPORT_SYMBOL(__module_get);
@@ -920,15 +918,11 @@ bool try_module_get(struct module *module)
 	bool ret = true;
 
 	if (module) {
-		preempt_disable();
-
 		if (likely(module_is_live(module))) {
-			__this_cpu_inc(module->refptr->incs);
+			this_cpu_inc(module->refptr->incs);
 			trace_module_get(module, _RET_IP_);
 		} else
 			ret = false;
-
-		preempt_enable();
 	}
 	return ret;
 }
@@ -937,15 +931,13 @@ EXPORT_SYMBOL(try_module_get);
 void module_put(struct module *module)
 {
 	if (module) {
-		preempt_disable();
 		smp_wmb(); /* see comment in module_refcount */
-		__this_cpu_inc(module->refptr->decs);
+		this_cpu_inc(module->refptr->decs);
 
 		trace_module_put(module, _RET_IP_);
 		/* Maybe they're waiting for us to drop reference? */
 		if (unlikely(!module_is_live(module)))
 			wake_up_process(module->waiter);
-		preempt_enable();
 	}
 }
 EXPORT_SYMBOL(module_put);


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