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: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/module.h b/include/linux/module.h
index 71f282a..ebfb0e1 100644 (file)
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -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

diff --git a/include/trace/events/module.h b/include/trace/events/module.h
index 7c5cbfe..81c4c18 100644 (file)
--- a/include/trace/events/module.h
+++ b/include/trace/events/module.h
@@ -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);
        ),
 

diff --git a/kernel/module.c b/kernel/module.c
index d596a30..b1d485d 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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();
        }