[PATCH 2/9] MTD: create lockless versions of {get,put}_mtd_device

Maxim Levitsky
2010-01-08T15:06:47Z

>From 1531249dd2c0e33d727ed8cbd0719eb4e9af2266 Mon Sep 17 00:00:00 2001
From: Maxim Levitsky <maximlevitsky@gmail.com>
Date: Fri, 8 Jan 2010 15:51:22 +0200
Subject: [PATCH 2/9] MTD: create lockless versions of {get,put}_mtd_device

This will be used to resolve deadlock in block translation layer.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
---
drivers/mtd/mtdcore.c | 61 ++++++++++++++++++++++++++++++-----------------
include/linux/mtd/mtd.h | 3 +-
2 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 87ff83f..96b4a05 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -454,27 +454,38 @@ struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)
ret = NULL;
}

- if (!ret)
- goto out_unlock;
-
- if (!try_module_get(ret->owner))
- goto out_unlock;
-
- if (ret->get_device) {
- err = ret->get_device(ret);
- if (err)
- goto out_put;
+ if (!ret) {
+ ret = ERR_PTR(err);
+ goto out;
}

- ret->usecount++;
+ err = __get_mtd_device(ret);
+ if (err)
+ ret = ERR_PTR(err);
+out:
mutex_unlock(&mtd_table_mutex);
return ret;
+}

-out_put:
- module_put(ret->owner);
-out_unlock:
- mutex_unlock(&mtd_table_mutex);
- return ERR_PTR(err);
+
+int __get_mtd_device(struct mtd_info *mtd)
+{
+ int err;
+
+ if (!try_module_get(mtd->owner))
+ return -ENODEV;
+
+ if (mtd->get_device) {
+
+ err = mtd->get_device(mtd);
+
+ if (err) {
+ module_put(mtd->owner);
+ return err;
+ }
+ }
+ mtd->usecount++;
+ return 0;
}

/**
@@ -525,18 +536,22 @@ out_unlock:

void put_mtd_device(struct mtd_info *mtd)
{
- int c;
-
mutex_lock(&mtd_table_mutex);
- c = --mtd->usecount;
- if (mtd->put_device)
- mtd->put_device(mtd);
+ __put_mtd_device(mtd);
mutex_unlock(&mtd_table_mutex);
- BUG_ON(c < 0);

module_put(mtd->owner);
}

+void __put_mtd_device(struct mtd_info *mtd)
+{
+ --mtd->usecount;
+ BUG_ON(mtd->usecount < 0);
+
+ if (mtd->put_device)
+ mtd->put_device(mtd);
+}
+
/* default_mtd_writev - default mtd writev method for MTD devices that
* don't implement their own
*/
@@ -570,7 +585,9 @@ EXPORT_SYMBOL_GPL(add_mtd_device);
EXPORT_SYMBOL_GPL(del_mtd_device);
EXPORT_SYMBOL_GPL(get_mtd_device);
EXPORT_SYMBOL_GPL(get_mtd_device_nm);
+EXPORT_SYMBOL_GPL(__get_mtd_device);
EXPORT_SYMBOL_GPL(put_mtd_device);
+EXPORT_SYMBOL_GPL(__put_mtd_device);
EXPORT_SYMBOL_GPL(register_mtd_user);
EXPORT_SYMBOL_GPL(unregister_mtd_user);
EXPORT_SYMBOL_GPL(default_mtd_writev);
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 0f32a9b..662d747 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -290,8 +290,9 @@ extern int add_mtd_device(struct mtd_info *mtd);
extern int del_mtd_device (struct mtd_info *mtd);

extern struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num);
+extern int __get_mtd_device(struct mtd_info *mtd);
+extern void __put_mtd_device(struct mtd_info *mtd);
extern struct mtd_info *get_mtd_device_nm(const char *name);
-
extern void put_mtd_device(struct mtd_info *mtd);

--
1.6.3.3