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module: Replace module_ref with atomic_t refcnt

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

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Masami Hiramatsu 2014-11-10 09:29:29 +10:30 committed by Rusty Russell
parent 0286b5ea12
commit 2f35c41f58
3 changed files with 7 additions and 50 deletions
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16
include/linux/module.h
View file

@ -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

2
include/trace/events/module.h
View file

@ -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);
),

39
kernel/module.c
View file

@ -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();
}