linux-kernel - [PATCHv2] module: kzalloc mod->ref

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Message-ID: <20090114055427.GN25103@bombadil.infradead.org>
Date:	Wed, 14 Jan 2009 00:54:27 -0500
From:	Kyle McMartin <kyle@...radead.org>
To:	Kyle McMartin <kyle@...radead.org>
Cc:	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org
Subject: [PATCHv2] module: kzalloc mod->ref

From: Kyle McMartin <kyle@...hat.com>

Dynamically allocate mod->ref instead of fixing it in the struct module.
Reduces on disk space wasted in the module .ko, and kills a loop
initializing the local_t it contains since we can just kzalloc it.

This matters when we're talking about large NR_CPUS.

Signed-off-by: Kyle McMartin <kyle@...hat.com>
---
The patch removing cacheline_aligned from struct module_ref should be
applied as well to cut down on the amount of memory we allocate. This
patch makes a nice stopgap until we have per_cpu module references.

I'm an idiot and forgot to kfree mod->ref last go 'round. refcount
doesn't look to be touched after module_unload_free, and since the
module unload code stop_machine_run with refcount at 0, it looks to be
as safe a place as any to nuke the array.

cheers, Kyle

diff --git a/include/linux/module.h b/include/linux/module.h
index 4f7ea12..5863998 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -345,7 +345,7 @@ struct module
 	void (*exit)(void);
 
 	/* Reference counts */
-	struct module_ref ref[NR_CPUS];
+	struct module_ref *ref;
 #endif
 };
 #ifndef MODULE_ARCH_INIT
diff --git a/kernel/module.c b/kernel/module.c
index c9332c9..8c8fe13 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -571,17 +571,19 @@ static char last_unloaded_module[MODULE_NAME_LEN+1];
 
 #ifdef CONFIG_MODULE_UNLOAD
 /* Init the unload section of the module. */
-static void module_unload_init(struct module *mod)
+static int module_unload_init(struct module *mod)
 {
-	unsigned int i;
+	mod->ref = kzalloc(NR_CPUS * sizeof(*mod->ref), GFP_KERNEL);
+	if (!mod->ref)
+		return -ENOMEM;
 
 	INIT_LIST_HEAD(&mod->modules_which_use_me);
-	for (i = 0; i < NR_CPUS; i++)
-		local_set(&mod->ref[i].count, 0);
 	/* Hold reference count during initialization. */
 	local_set(&mod->ref[raw_smp_processor_id()].count, 1);
 	/* Backwards compatibility macros put refcount during init. */
 	mod->waiter = current;
+
+	return 0;
 }
 
 /* modules using other modules */
@@ -661,6 +663,8 @@ static void module_unload_free(struct module *mod)
 			}
 		}
 	}
+
+	kfree(mod->ref);
 }
 
 #ifdef CONFIG_MODULE_FORCE_UNLOAD
@@ -919,8 +923,9 @@ static inline int use_module(struct module *a, struct module *b)
 	return strong_try_module_get(b) == 0;
 }
 
-static inline void module_unload_init(struct module *mod)
+static inline int module_unload_init(struct module *mod)
 {
+	return 0;
 }
 #endif /* CONFIG_MODULE_UNLOAD */
 
@@ -2071,7 +2076,9 @@ static noinline struct module *load_module(void __user *umod,
 	mod = (void *)sechdrs[modindex].sh_addr;
 
 	/* Now we've moved module, initialize linked lists, etc. */
-	module_unload_init(mod);
+	err = module_unload_init(mod);
+	if (err < 0)
+		goto free_unload;
 
 	/* add kobject, so we can reference it. */
 	err = mod_sysfs_init(mod);
--
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