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>

3 files changed, 7 insertions, 50 deletions

diff --git a/include/linux/module.h b/include/linux/module.h
index 71f282a4e307..ebfb0e153c6a 100644
--- 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 7c5cbfe3fc49..81c4c183d348 100644
--- 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 d596a306b0a1..b1d485df5ac1 100644
--- 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();
         }