module: Replace module_ref with atomic_t refcnt

Replace module_ref per-cpu complex reference counter with an atomic_t simple refcnt. This is for code simplification.

Masami Hiramatsu committed 12 years ago

Commit 2f35c411 parent 0286b5e3 files · +7 −50Browse files

Unified · Split

3 files

include/linux/module.h +1 −15
include/trace/events/module.h +1 −1
kernel/module.c +5 −34

@@ -210,20 +210,6 @@ enum module_state { · 209 unmodified lines
210	MODULE_STATE_UNFORMED, /* Still setting it up. */	210	MODULE_STATE_UNFORMED, /* Still setting it up. */
211	};	211	};
212		212
213	/**
214	* struct module_ref - per cpu module reference counts
215	* @incs: number of module get on this cpu
216	* @decs: number of module put on this cpu
217	*
218	* We force an alignment on 8 or 16 bytes, so that alloc_percpu()
219	* put @incs/@decs in same cache line, with no extra memory cost,
220	* since alloc_percpu() is fine grained.
221	*/
222	struct module_ref {
223	unsigned long incs;
224	unsigned long decs;
225	} __attribute((aligned(2 * sizeof(unsigned long))));
226
227	struct module {	213	struct module {
228	enum module_state state;	214	enum module_state state;
229		215
@@ -367,7 +353,7 @@ struct module { · 137 unmodified lines
367	/* Destruction function. */	353	/* Destruction function. */
368	void (*exit)(void);	354	void (*exit)(void);
369		355
370	struct module_ref __percpu *refptr;	356	atomic_t refcnt;
371	#endif	357	#endif
372		358
373	#ifdef CONFIG_CONSTRUCTORS	359	#ifdef CONFIG_CONSTRUCTORS

include/trace/events/module.h+1−1

@@ -80,7 +80,7 @@ DECLARE_EVENT_CLASS(module_refcnt, · 79 unmodified lines
80		80
81	TP_fast_assign(	81	TP_fast_assign(
82	__entry->ip = ip;	82	__entry->ip = ip;
83	__entry->refcnt = __this_cpu_read(mod->refptr->incs) - __this_cpu_read(mod->refptr->decs);	83	__entry->refcnt = atomic_read(&mod->refcnt);
84	__assign_str(name, mod->name);	84	__assign_str(name, mod->name);
85	),	85	),
86		86

kernel/module.c+5−34

 /* Init the unload section of the module. */
 static int module_unload_init(struct module *mod)
 {
-	mod->refptr = alloc_percpu(struct module_ref);
-	if (!mod->refptr)
-		return -ENOMEM;
 	INIT_LIST_HEAD(&mod->source_list);
 	INIT_LIST_HEAD(&mod->target_list);
 	/* Hold reference count during initialization. */
-	raw_cpu_write(mod->refptr->incs, 1);
+	atomic_set(&mod->refcnt, 1);
 	return 0;
 }
 		kfree(use);
 	}
 	mutex_unlock(&module_mutex);
-	free_percpu(mod->refptr);
 }
 #ifdef CONFIG_MODULE_FORCE_UNLOAD
 unsigned long module_refcount(struct module *mod)
 {
-	unsigned long incs = 0, decs = 0;
+	return (unsigned long)atomic_read(&mod->refcnt);
-	int cpu;
-	for_each_possible_cpu(cpu)
-		decs += per_cpu_ptr(mod->refptr, cpu)->decs;
-	/*
-	 * ensure the incs are added up after the decs.
-	 * module_put ensures incs are visible before decs with smp_wmb.
-	 *
-	 * This 2-count scheme avoids the situation where the refcount
-	 * for CPU0 is read, then CPU0 increments the module refcount,
-	 * then CPU1 drops that refcount, then the refcount for CPU1 is
-	 * read. We would record a decrement but not its corresponding
-	 * increment so we would see a low count (disaster).
-	 *
-	 * Rare situation? But module_refcount can be preempted, and we
-	 * might be tallying up 4096+ CPUs. So it is not impossible.
-	 */
-	smp_rmb();
-	for_each_possible_cpu(cpu)
-		incs += per_cpu_ptr(mod->refptr, cpu)->incs;
-	return incs - decs;
 }
 EXPORT_SYMBOL(module_refcount);
 {
 	if (module) {
 		preempt_disable();
-		__this_cpu_inc(module->refptr->incs);
+		atomic_inc(&module->refcnt);
 		trace_module_get(module, _RET_IP_);
 		preempt_enable();
 	}
 		preempt_disable();
 		if (likely(module_is_live(module))) {
-			__this_cpu_inc(module->refptr->incs);
+			atomic_inc(&module->refcnt);
 			trace_module_get(module, _RET_IP_);
 		} else
 			ret = false;
 {
 	if (module) {
 		preempt_disable();
-		smp_wmb(); /* see comment in module_refcount */
+		atomic_dec(&module->refcnt);
-		__this_cpu_inc(module->refptr->decs);
 		trace_module_put(module, _RET_IP_);
 		preempt_enable();
 	}

module: Replace module_ref with atomic_t refcnt

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