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Commit 2f35c41f authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Rusty Russell
Browse files

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.

Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 0286b5ea

include/linux/module.h

+1 −15
Original line number Diff line number Diff line
@@ -210,20 +210,6 @@ enum module_state { 
	MODULE_STATE_UNFORMED,	/* Still setting it up. */

};



/**

 * struct module_ref - per cpu module reference counts

 * @incs: number of module get on this cpu

 * @decs: number of module put on this cpu

 *

 * We force an alignment on 8 or 16 bytes, so that alloc_percpu()

 * put @incs/@decs in same cache line, with no extra memory cost,

 * since alloc_percpu() is fine grained.

 */

struct module_ref {

	unsigned long incs;

	unsigned long decs;

} __attribute((aligned(2 * sizeof(unsigned long))));



struct module {

	enum module_state state;
@@ -367,7 +353,7 @@ struct module { 
	/* Destruction function. */

	void (*exit)(void);



	struct module_ref __percpu *refptr;

	atomic_t refcnt;

#endif



#ifdef CONFIG_CONSTRUCTORS

include/trace/events/module.h

+1 −1
Original line number Diff line number Diff line
@@ -80,7 +80,7 @@ DECLARE_EVENT_CLASS(module_refcnt, 


	TP_fast_assign(

		__entry->ip	= ip;

		__entry->refcnt	= __this_cpu_read(mod->refptr->incs) - __this_cpu_read(mod->refptr->decs);

		__entry->refcnt	= atomic_read(&mod->refcnt);

		__assign_str(name, mod->name);

	),

kernel/module.c

+5 −34
Original line number Diff line number Diff line
@@ -631,15 +631,11 @@ EXPORT_TRACEPOINT_SYMBOL(module_get); 
/* 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;

}
@@ -721,8 +717,6 @@ static void module_unload_free(struct module *mod) 
		kfree(use);

	}

	mutex_unlock(&module_mutex);



	free_percpu(mod->refptr);

}



#ifdef CONFIG_MODULE_FORCE_UNLOAD
@@ -772,28 +766,7 @@ static int try_stop_module(struct module *mod, int flags, int *forced) 


unsigned long module_refcount(struct module *mod)

{

	unsigned long incs = 0, decs = 0;

	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;

	return (unsigned long)atomic_read(&mod->refcnt);

}

EXPORT_SYMBOL(module_refcount);
@@ -935,7 +908,7 @@ void __module_get(struct module *module) 
{

	if (module) {

		preempt_disable();

		__this_cpu_inc(module->refptr->incs);

		atomic_inc(&module->refcnt);

		trace_module_get(module, _RET_IP_);

		preempt_enable();

	}
@@ -950,7 +923,7 @@ bool try_module_get(struct module *module) 
		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;
@@ -965,9 +938,7 @@ void module_put(struct module *module) 
{

	if (module) {

		preempt_disable();

		smp_wmb(); /* see comment in module_refcount */

		__this_cpu_inc(module->refptr->decs);



		atomic_dec(&module->refcnt);

		trace_module_put(module, _RET_IP_);

		preempt_enable();

	}